So I can't stop playing. I actually love this game. If it weren't for the short-but-sweet 8-hour campaign, I'd be sitting at my computer for DAYS. I was never a gamer nerd, but if I were, I think it would feel similar to this.
Anyway, for the non-PC gamers like me, let me briefly explain what it is. Portal 2 is a very well-balanced and thought-out first person puzzle game. You basically use a portal making device to create 2-way portals to open doors and press buttons to get through the level, with the help of blocks, lasers, liquid gels, transfer beams, and launching devices.
The levels are actually challenging, but not to a point where they become extremely difficult to solve. I don't think I've spent a HUGE amount of time solving a test, so in my opinion, the levels aren't as hard as they look at first and are pretty well balanced between solvability (yeah, it's not a word) and complexity. Some are pretty tricky, but once you get the hang of it and know the advantages of making portals, it comes fairly easy to manage a test. Here are some screens:
Here's demo video of one of the trickiest levels in the game.
This one actually took me about 30-35 minutes until I found out
that the tractor beam thing can run through screens.
I guess you'll know what I'm talking about once you try it.
Keep the mind in check. Play this.