Amazing, equalled only by it's predecessor. Riven adds great things to an already fantastic series.
On the surface, the game seems simple enough, just your average Adventure/Puzzler, but it is so much deeper. The game featured incredible graphics and mechanics for its time, and you could interact with almost any object in the game.
As the story progresses, you learn more and more about your character, like most games, but there is almost no character interaction, since the only person who speaks to you is a pre-recorded hologram.
Apart from this hologram, the only other times you see people are when you catch glimpses of the island's natives, but they swiftly run away before you get anywhere near them. Now for some games, the lack of other characters might make it seem hollow and boring, but in Riven it just increases the suspense and mystery of the island you are trapped on, and the fleeting glances you get just confirm whatever suspicions you have that you are being watched.
The game gives you great replay value as well, because each time you play it, doing something slightly different, or in a different order, will completely affect your future on the island. Some puzzles do not allow you to go back once you get past them, so you are committed to whatever course of action you have chosen. The multiple endings are unique and involving, but will leave you wanting to go back and find out what could have been done differently.
The downsides of the game are few, and are not all bad. One annoying thing is that certain problems leave you no option but to solve them, and they can get mighty hard at times, and may have you searching for a game guide. Also, the fact that you get forced to to continue once you pass certain points can be frustrating, because you can sometimes leave things that you want to come back and do later. This is why it pays to save often in Riven, so you don't get trapped by the island's tricks.
For those trigger-happy, all action types out there, I would advise you to steer clear. But for those more intellectual souls out there, this game will put all of your logic and lateral thinking to the test, and the suspense and atmosphere will leave you guessing.
So, all up the game is fantastic, and leaves you with a feeling of satisfaction and fulfillment when finished, and the experience will have you going back for more.