I have a couple questions. Is spacechem challenging? I have never bought it because it said casual, and I have been burned before by puzzle games meant for children. I do like puzzles, though, and if it's hard, I'm in.
SpaceChem starts out pretty easy and obvious in the first few levels just to explain the mechanics, but after that, you're pretty much on your own. Once it tells you what all the buttons do, it expects you to figure out how to take advantage of the mechanics entirely on your own. You can do some really crazy things once you do figure out how they work, and in the later levels you pretty much have to. If you start competing for the leaderboards for best solutions (fewest pieces used, shortest time, etc.), it quickly reaches completely preposterous levels of complexity. Try the demo, and make sure you get past the tutorial levels to where there's a jump in difficulty. Then keep in mind that there are several more jumps like that throughout the game, and if that sounds like fun, you'll like the full game.
Also, about the second game, I never purchased it because I similarly had some preconceptions about the game. I didn't realize it was a sandbox shooter. Maybe I should learn a bit more about it.
I totally didn't think I was going to like it at all when I first heard about it, but I'd seen a couple good reviews of it, and it was on sale really, really cheap one day (might've been the Steam holiday sale last winter, actually), so I bought it on a whim not expecting much from it, and it turned out to be surprisingly fun. The setting is kind of a cross between North Korea and a Southeast Asian island, and the tone of the game is basically reenacting the movie Team America, liberating the people to death by blowing up the entire place, because explosions are fun. It's a very silly game, but there's something to be said for flying around with your grappling hook/parachute raining bullets and grenades on unsuspecting guards that makes you feel like the Latino version of Batman. If he didn't have a thing against guns. Heh.