Firstly i'm going to say that this post does contain Portal 2 spoilers.
I'm quite surprised at the number of Brink players assuming that EVERYONE who say's that they've heard bad things about Brink must be a Valve "fanboy". Personally, no, I haven't played Brink, but from what my close friends have told me, this is pretty much it:
1) It's too short, apparently you get all of the unlockables within around a days play.
2) "Lone wolf" type players really ruin it for everyone else
3) Single player is bad because of the bots AI.
4) It is fun, given you get the right type of players on your team
5) There are lag/fps issues.
It does sound good, despite it's flaws, but as a lot of people have pointed out, the main flaw with it appears to be the players themselves. Too many people playing with a Call of Duty attitude.
I have played Portal 2 myself, and honestly, yeah. I loved every second. Sure, it's a short game, really short by today's standards. But quite honestly I take quality over quantity. I still think it's brilliant, despite it's lack of replay value. I think it was a funny game with a really strong sense of atmosphere as well, with characters you really do become attatched to. I loved Wheatley from start to finish, and even GLaDOS becomes likeable once she's put into a potato.
And i'd just like to say, i'm by no means a "Valve fanboy". The only games by Valve i've ever bought have been The Orange Box and Portal 2. And I still haven't even done Half Life episode 1 or 2 yet, played very little of TF2 since no one is ever on it on the Xbox it seems.