Borderlands is a good game, but it have a huge pile of small nitpicks.
The game is "console'd". If you love playing console FPS you may not mind, but if you was born and raised with a keyboard, it may turn your down a bit. I only started to enjoy the game after I edited some .ini files to force the game to play like I wanted, instead of the other way around.
While the game is fun, I find it slow... it's like everybody is a TF2 Heavy. While I found all the 4 characters interesting, there isn't that much difference of havnig one or another on your team. The gun's define the characters, and everybody can use any gun.
And talking about guns, while there is "bazillion" of them, they are mostly "bullet" gun. No grenade launchers, no mine layers, no flamethrowers, etc, etc.
And to my surprise, I found you can use your single player character on multiplayer.. isn't this a bit cheating prone?
But complains aside, it's a good game, worth the price, They can't make everybody happy, but will probably make most of them.