Short answer
Paradise in Islam is a garden of endless joy, lived in forever. The Qur'an describes gardens with rivers flowing beneath them, as wide as the heavens and the earth. There is no sorrow, tiredness or death there, and no bitterness is left in anyone's heart. Its people have all they wish for, and more. The Prophet Muhammad (ﷺ) said it holds what no eye has seen and no ear has heard. He said a space in it the size of a foot is better than the whole world. A believer who had the hardest life on earth, dipped in it once, will say he never knew hardship. The greatest joy of all is that God (﷾) is pleased with its people. A person enters it by God's (﷾) mercy, which he seeks through faith and good deeds.
Full explanation
Gardens as wide as the heavens and the earth
The Qur'an promises believers who do good an eternal home in gardens with rivers flowing beneath them. The gardens are as wide as the heavens and the earth. It speaks of rivers of water that never spoils, milk whose taste never changes and pure honey. It also speaks of wine that is a joy to those who drink. This wine never makes them drunk and never gives them a headache. There is every kind of fruit.
“But give glad tidings to those who believe and work righteousness, that their portion is Gardens, beneath which rivers flow. Every time they are fed with fruits therefrom, they say: "Why, this is what we were fed with before," for they are given things in similitude; and they have therein companions pure (and holy); and they abide therein (for ever).”
“Be ye foremost (in seeking) Forgiveness from your Lord, and a Garden (of Bliss), the width whereof is as the width of heaven and earth, prepared for those who believe in Allah and His messengers: that is the Grace of Allah, which He bestows on whom he pleases: and Allah is the Lord of Grace abounding.”
“But those who believe and do deeds of righteousness, We shall soon admit to Gardens, with rivers flowing beneath,- their eternal home: Therein shall they have companions pure and holy: We shall admit them to shades, cool and ever deepening.”
“(Here is) a Parable of the Garden which the righteous are promised: in it are rivers of water incorruptible; rivers of milk of which the taste never changes; rivers of wine, a joy to those who drink; and rivers of honey pure and clear. In it there are for them all kinds of fruits; and Grace from their Lord. (Can those in such Bliss) be compared to such as shall dwell for ever in the Fire, and be given, to drink, boiling water, so that it cuts up their bowels (to pieces)?”
“Free from headiness; nor will they suffer intoxication therefrom.”
“No after-ache will they receive therefrom, nor will they suffer intoxication:”
No sorrow, no tiredness, no death
Everything that spoils happiness on earth is absent. God (﷾) removes every grudge from the hearts of its people, so they meet as brothers. They feel no tiredness, never fall ill or grow old, and are never asked to leave. They thank God (﷾) for taking away all sorrow, and they never taste death again.
“The righteous (will be) amid gardens and fountains (of clear-flowing water). (Their greeting will be): "Enter ye here in peace and security." And We shall remove from their hearts any lurking sense of injury: (they will be) brothers (joyfully) facing each other on thrones (of dignity). There no sense of fatigue shall touch them, nor shall they (ever) be asked to leave.”
“And they will say: "Praise be to Allah, Who has removed from us (all) sorrow: for our Lord is indeed Oft-Forgiving Ready to appreciate (service): "Who has, out of His Bounty, settled us in a Home that will last: no toil nor sense of weariness shall touch us therein."”
“Nor will they there taste Death, except the first death; and He will preserve them from the Penalty of the Blazing Fire,-”
Abu Sa'id al-Khudri and Abu Hurayra report that the Prophet (ﷺ) said a caller will announce to the people of Paradise that they will be healthy and never fall ill, live and never die, stay young and never grow old, and enjoy comfort and never know hardship.
Spouses pure and holy
The Qur'an says the people of Paradise will have companions pure and holy, and that God (﷾) will join them to spouses of great beauty. It gives no number.
“But give glad tidings to those who believe and work righteousness, that their portion is Gardens, beneath which rivers flow. Every time they are fed with fruits therefrom, they say: "Why, this is what we were fed with before," for they are given things in similitude; and they have therein companions pure (and holy); and they abide therein (for ever).”
“But those who believe and do deeds of righteousness, We shall soon admit to Gardens, with rivers flowing beneath,- their eternal home: Therein shall they have companions pure and holy: We shall admit them to shades, cool and ever deepening.”
“So; and We shall join them to fair women with beautiful, big, and lustrous eyes.”
What no eye has seen
The Prophet (ﷺ) said that God (﷾) has prepared something for His righteous servants. No eye has seen it, no ear has heard of it and no heart has imagined it. He recited the verse that says no soul knows the joys kept hidden for it. The Qur'an adds that its people will have all they wish for, and more.
Abu Hurayra reports that the Prophet (ﷺ) said God has declared: I have prepared for My righteous servants what no eye has seen, no ear has heard, and no human heart has imagined. The report then invites the listener to recite Qur'an 32:17: no soul knows what joy is kept hidden for them.
Sahl ibn Sa'd reports that the Prophet (ﷺ) described Paradise and ended by saying it holds blessings no eye has seen, no ear has heard, and no human heart has ever imagined. He then recited Qur'an 32:16-17.
“Now no person knows what delights of the eye are kept hidden (in reserve) for them - as a reward for their (good) deeds.”
“There will be for them therein all that they wish,- and more besides in Our Presence.”
How great it is
The Prophet (ﷺ) said the lowest person in Paradise will have the like of the whole world, and ten times more. A space in it the size of a foot is better than the world and everything in it. Take the believer who had the most miserable life on earth. Dipped in Paradise once, he will swear he never knew any hardship at all.
Abdullah ibn Mas'ud reports that the Prophet (ﷺ) described the last man to come out of the Fire and enter Paradise. Each time he goes to it, it seems full to him. Then God tells him that he has the like of the whole world and ten times as much. The report adds that this was said to be the lowest rank among the people of Paradise.
Al-Mughira ibn Shu'ba reports that the Prophet (ﷺ) said Moses asked God who has the lowest rank in Paradise. God said it is the last man to enter it, who is offered the like of a worldly king's kingdom, five times over, and then ten times as much, with whatever his soul desires and his eye delights in.
Anas reports that when a mother grieved for her son killed at Badr, the Prophet (ﷺ) told her that there are many gardens in Paradise and her son was in the highest, al-Firdaws. He added that a space in Paradise as small as a bow's length or a foot is better than the whole world and all it holds.
Anas ibn Malik reports that the Prophet (ﷺ) said the person who had the most comfortable life on earth, if he is among the people of the Fire, will be dipped in it once and will say he never knew any comfort. And the person who had the most miserable life on earth, if he is among the people of Paradise, will be dipped in it once and will swear to his Lord that he never knew any hardship or distress.
The greatest joy: God (﷾) is pleased with them
Paradise is more than pleasure. The Qur'an says the greatest bliss of all is the good pleasure of God (﷾). Its people's words there are praise of God (﷾), and their greeting to each other is "Peace".
“Allah hath promised to Believers, men and women, gardens under which rivers flow, to dwell therein, and beautiful mansions in gardens of everlasting bliss. But the greatest bliss is the good pleasure of Allah: that is the supreme felicity.”
“Those who believe, and work righteousness,- their Lord will guide them because of their faith: beneath them will flow rivers in gardens of bliss. (This will be) their cry therein: "Glory to Thee, O Allah!" And "Peace" will be their greeting therein! and the close of their cry will be: "Praise be to Allah, the Cherisher and Sustainer of the worlds!"”
How Paradise is entered
The Prophet (ﷺ) taught that no one's deeds will save him. Asked if this was true of him too, he said: not even me, unless God (﷾) covers me with His mercy. Paradise is prepared for those who believe in God (﷾) and His messengers, and faith and good deeds are how a servant seeks that mercy.
Abu Hurayra reports that the Prophet (ﷺ) said no one's deeds will save him. Asked whether that included him, he said: not even me, unless Allah covers me with His mercy. He then told them to do good deeds properly, sincerely and in moderation.
“Be ye foremost (in seeking) Forgiveness from your Lord, and a Garden (of Bliss), the width whereof is as the width of heaven and earth, prepared for those who believe in Allah and His messengers: that is the Grace of Allah, which He bestows on whom he pleases: and Allah is the Lord of Grace abounding.”
“But those who believe and do deeds of righteousness, We shall soon admit to Gardens, with rivers flowing beneath,- their eternal home: Therein shall they have companions pure and holy: We shall admit them to shades, cool and ever deepening.”
Perspectives
The Islamic perspective
Paradise is an eternal garden of joy, with no sorrow, sickness or death. The Qur'an and the Prophet (ﷺ) describe it as greater than anything the mind can picture. Its highest joy is God's (﷾) good pleasure, and it is entered by His mercy.
The Qur'an promises believers who do good an eternal home in gardens with rivers flowing beneath. The gardens are as wide as the heavens and the earth.
In Paradise there is no grudge, tiredness, sorrow, sickness or death, and no one is ever made to leave.
Its joys are beyond anything seen, heard or imagined, and its people have all they wish for and more.
The Prophet (ﷺ) said the lowest rank in Paradise has ten times the like of this world. He also said a foot's space in it is better than the whole world.
The believer who had the most miserable life on earth will be dipped in Paradise once. It will make him forget every hardship he knew.
Paradise is not only bodily pleasure: the Qur'an names God's good pleasure as its greatest bliss.
Paradise is entered by God's (﷾) mercy, not bought by deeds. Faith and good deeds are how a servant seeks that mercy.