I have what may be a silly question... what color depth should Riven be running in? For some reason, I thought it was greater than 256 colors, but it seems that theres massive amounts of dithering (the scene with Atrus when you load the game has lines all over it). Am I just remembering better graphics in my head then the game actually had?
edit: hmm... perhaps its a problem of resolution scaling with the LCD causing the dithering to look worse.. if I turn off run in 640x480 mode, the game does look noticebly better when playing without scaling... still not as good as my minds eye remembers, but better.

That sounds like your game is having an issue. Can you post your specs and also if you don't mind taking a screenshot (Print screen button) that would be great.
That might be it, but take a screenshot just to be safe. I also have a LCD monitor and I'm not sure I noticed what you are describing.

Heres the image... as I said, it's not as noticeable when at native 640x480, but you can still see the vertical banding the dithering causes. I thought the game ran at a higher resolution than 256 colors...

I think I remember seeing that sort of thing during the video scenes, but not the stills. Otherwise though it looks normal compared to mine.

I have the same problem. The game seems to be using 256 colors only. Look at the attached picture and notice the dithering. You can even load the image up in a image editing package to count the colors, which definitely shows no more than 256 colors are used.

Same here. It really doesn't look like more than 256 colors. Here is an image of the game, it's at 150% sure, but that's how it looks like when the game uses your screen and doesn't just occupy one tenth of it in the middle in its native 640 resolution. Anyway, even at the 640 resolution you can see this if you look closely...

and can anyone help me with this? the videos works just fine, but when the game starts for real, it looks like this -_-' I'm on Linux by the way if it changes something...