The quickie review is: Just like JotO, but less of it and not as good. And Chinese, instead of faux-Mesopotamian.
First of all, there are fourteen puzzles, as opposed to 24 in JotO. And they were less clever. I don't remember the full list, but I think there is a higher percentage of straight-out-of-the-book classic puzzles. A couple of the puzzles were timed -- they had an element of hand-eye coordination, and if you weren't quick on the mouse, you failed. Bleah.
The art is still nice, although there's half as much of it, and I didn't have the same feeling of really careful attention to detail. (JotO had dirt. I love dirt. Everything was worn and chipped. Karma just looked a little fuzzy.)
My other big complaint was that the movies didn't play well on my 4x-CD 9500. What? Honest. They were much too fast. Don't ask me what went wrong; QuickTime can certainly handle correct frame rates on a fast processor. But many of the traversal movies were like, zip zip! It really ruined the mood. JotO was this stately solemn ancient temple, and yes, it was too slow and jagged on my 2x-CD 68040 Centris, but the Discis people shouldn't have made the optimal speed as fast as Karma is. (I guess I should try JotO on the 9500 and Karma on the Centris. Hm.)
Plus, I finished Karma in two play sessions. Except for one puzzle, the good old goddam sliding-block puzzle (move the 2x2 block from the top to the bottom) -- that one was much harder than all the others. (Even looking at the on-line hints, which just said "move the 2x2 block from the top to the bottom." Which was obvious anyway.) I cheated and hacked the save file; I hate that puzzle. JotO took me three or four times as long -- even if you ignore the two very difficult puzzles in that game.
And JotO had that weird element of revealing more and more about the culture of the people who had built the temple. It never became relevant, but I liked it. Had some depth. Karma doesn't have any of that.
Conclusion: If you thought JotO was worthwhile, pay half as much for Karma. If you hated JotO, skip Karma.