Like the other games in the Horizons line, it stands the d20 engine on it's head. I think part of the concept was to push the rules in new & creative ways. Mechamorphosis is actually the one I understand the least in that line, but any of them are a good little read at 64 pages. I find it very interesting to see the application of the d20 system to genres other than sword-and-sorcery fantasy.
I ran Spellslinger as a mini-camapign. It was interesting, but I think I could more easily extrapolate a lower-magic Western D&D game from the core rules if I were to do it again. I might just use the NPC classes from the DMG with PCs being either Experts or Warriors (or both--maybe gestalt). But, Spellsinger is flexible enough that you could just take the parts you wanted and leave the rest out. I wanted to see a feat-based magic system in action. It was cool.
I would like to run the Grimm adventure I downloaded. I don't think I could really get my players interested for it, much less a campaign. The book is a great read, though. The dark tone of fairy tales really shines through. I was even inspired to check out a copy of Grimm's Tales at the local library and read parts of it.
Redline has too much competition from other post-apocalyptic games that I have. It would be great as a Mad Max style game without the creep (mutations).
Virtual doesn't really appeal to me as a sort of game-within-a-game. The text is an interesting delve into some online concepts, though.
