I can attest that VVVVVV is really, really challenging, and quite fun. It's so satisfactory when you beat a hard level or get a particularly difficult gem.
Has anyone played any of the other games in this pack? I'll prob end up getting this bundle anyway, since I've gotten every other one so far (even tho the frozen byte one included some non-linux games) and enjoyed at least one game incredibly thoroughly in all of them, but I just wanna know some personal opinions on the games.