You should play Single Player first
Yeah I will
but I love the look of co-op
I may well get it, and it would be through steam if I do. I'm just going to wait for the prices to go down a bit first since I got Portal 1 recently and have only spent about 2 hours playing it.
Grabbed it, might play it later tonight. It definitely looks slick, heard good things about it. The original one was just fantastic.