Black market is fun for a little while. It's not a complex game, it's a pretty simple flash game. You can try their web version of it out a bit, if you like that then you'll like the full version (it's just more of the same kind of stuff, continuing the story). I got it in the first bundle and played through it. I think it took me around 5 or 6 hours? I didn't have many crashes though, and I kind of rushed through it. It was more entertaining than a lot of movies I've paid more to see, so to me it was worth it.
AirBuccaneers is a novel cooperative first person shooter with you flying airships with cannons. You can play that one free while it's in alpha (although I think you're limited? not sure how that works, I just grabbed it and activated mine immediately). I find it pretty entertaining - more lasting appeal than Black Market at least, since it's multiplayer.
Devil Whiskey is OK if you like that type of game. I found the way the game handles random encounters to be a bit tedious (just randomly putting you up against monsters every few steps, everywhere you go, even inside town, with no limit to them so you can't clear a place out), but otherwise it's an interesting game with lots of dungeon to explore. It's probably a pretty niche market, so I'd recommend trying the demo on GG before getting it. If you do like it you could sink quite a few hours into it.
I personally also bought Star Prospector, 3079, Telepath, and Demise because they sounded interesting - but I haven't played them yet (except 3079, which I haven't really played enough to comment on it). A friend of mine is telling me that Star Prospector is "awesome", but he's steered me wrong in the past (Spore is awesome?) so i'm not sure if that says much
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I believe some of the cheaper ones are more coffee break diversions than engrossing games. To be honest though, at a mere $1 per game you can hardly go wrong with even the shortest coffee break games. Even if I chuck it after a day or two, a few hours of solid enjoyment is easily worth a buck to me.