Played yesterday a few hours in coop (I think approx 5 hours) and we finished 3 puzzle chapters and the 4th seems to be the last one. Didn't started the sp yet.
So the game seems to be reasonable short, which doesn't really surprise me, though. The big problem is just the replayability. If you know the puzzles, you can solve them in a very short time and this results then in loading screen, loading screen, loading screen, loading screen, loading screen... because every puzzle has it's own map and if you are done, the next one is loaded. The loading times are fast, but it's still a bit annoying.
So far, the game is fun, but the difficult curve in the coop is a bit meh. Sometimes there is a puzzle that you solve in a very short time and then there is a puzzle where you can go rampage, because you don't figure out the obvious. The next puzzle then is really easy again, etc. I dunno, but so far there hasn't been any super big and complex puzzle in coop. Everything was possible to solve in a reasonable amount of time and without much thinking. There are more than enough hints in a map to get it done fast.
And yeah, about the shop: What the fuck. 5 euro for a different texture. 3 euro for some shitty hat that nobody needs anyway. What the fuck. Especially in a game with so little replayability, who is this stupid to pay for tiny details that nobody really cares about? I don't get it. In TF2 I can still somewhat understand it, because some folks play it a lot for a very long time... But Portal 2, if you are done once, you will never replay it like a TF2 game.
Really, the whole Portal 2 deal is a pure money crimper. First the pre-release "buy games for 33 euro to get the game faster!" only to have the game max. 13 hours faster (which is like nothing for me personally. It got released in the morning when I was on my way to work, so I couldn't play it earlier anyway). And then this item shop... VALVe is trying way too hard here. Way too hard...