Finally an Indie bundle where I don't already own even one of the games! I'm jumping on this bundle, it's a great price considering I have heard good things about most of them, and they're all games I've been curious about.
Gridrunner and Space Giraffe are two I've been eyeing for a while, but they have been hovering around $15-$20 for the last year -- I assumed they'd go on sale eventually, after being added to Steam a few days ago, but not this cheap and this soon! They're by Jeff Minter, which should be a familiar (retro) name to quite a few, and there's been quite a lot of love for them on the various indie-friendly sites.
Bob Came In Pieces has gotten pretty good reviews too. Playing the demo, I was disappointed that it didn't have a thruster/lunar lander control feel to it, but was instead more a platformer with unlimited jump height. But I can see how adding heavy gravity and momentum would make it a totally different game than the puzzle game they're going for.
I've heard decent things about all of the others, not of universally loving praise for all of them, but still good, and would have considered any of them if they'd popped up at $2 by themselves. I don't think any of the games in this pack have had the breaking-into-the-mainstream success of titles like World of Goo or Braid, but they're all fairly well known indie titles, not just filler. Altitude was Steam's top selling under-$10 title after it came out, and Galcon Fusion is the sequel to an IGF Mobile winner that has been doing quite well on the iPhone and as a Flash game on the web, for example.
But if you're just looking at Bullet Candy you can get the newer improved Bullet Candy Perfect
straight from the author for any price you want, starting at $1. It's basically the same game, but with improved graphics and compatibility, so it's probably a better choice than the old version on Steam.