I recently bought the game Trine in a 3-game bundle on steam, 3 games for 5 euro, saving 40. Though I did this simply because I was interested in the game Trine in the bundle, and it turns out this is one of the best games I've ever played. I can't believe I've never bought this game until now!
Trine has you take on puzzle solving alá Portal, but in a side-scrolling fantasy adventure. The aesthetics of the game are amazing with bright and vivid colors. The story, though it might not be amazingly deep, is still compelling and the world intruiging. The puzzles are challenging but not frustrating, though I've just played it on Easy so far. It involves combat as well with both minions and big boss fights that require some thinking to beat.
The game makes heavy use of it's physics engine for both combat and puzzle solving, if you swing across ledges, time a jump from a pendulum, create crates or planks to balance weights or traverse heights, or shoot arrows at ropes to send a stonefist flying against a wall.
But as said, most of all this game is mind-blowingly gorgeous. And when it costs you 5 euros and gets you 2 more games with it, it is definetly the most bang-per-buck I've ever gotten.
Here are some screenshots from when I've been playing.
I talked to a Steam friend, who had also bought the game with this bundle, when he mentioned that they are doing a sequel aptly named Trine 2.
Here's the trailer for the even more mind-blowingly gorgeous Trine 2 http://trine2.com/
If you like side-scrollers, fantasty and puzzle solving this game is DEFINETLY for you! And even if you don't, I'm quite sure it won't hurt buying the 3-game bundle for 5 Euro.