Without doing any kind of research about it,of what it's purpose is and not bothering to find any info about it's mechanics philosophy.
Thus entering a "trap" if you like and feeling disappointed or furstrated that it's not what they have used or learned to play.
It can be a fast-paced game but here (in BRINK) it doesn't matter how fast you go to engage the enemy but how well prepared/organised and smart you go.
They were also disappointed by the fact that objectives are in one place or in a room,thus making it without meaning for them to run around and just shooting without purpose.
These facts just point to the obvious direction it's Developers said many & many & many times in many & many & many interviews expaining in common language what this game is:
A team-oriented,objective-based FPS game,so simple yet so hard to coprehent apparently.
So these facts plus the lag lead to some bad reviews,still these reviews are not enough to show the obvious truth,from all reviews an average of 7.5 to 7.6 is a success,to me at least.
I haven't seen/played a perfect/flawless game in my lifetime (i'm 35 yo),still many talk about games as they should be http://en.wikipedia.org/wiki/Shangri-La.
BRINK has it's flaws as any other game i know and even more Splash Damage is not a colossal Developing team like others... . .
After that it all goes down to the Developers again,for this as for any other game again,to continue the effort and devotion of suporting the game.
As for me,thank you very much for this game!
P.S.: I also feel that is common sense that every new game,even more if it has new/different mechanics,needs more than just an hour of gameplay to get the hang of it,
thus not to be furstrated for losing so easyly.
And as far as i know lag is something that can be fixed.
We must start thinking before talking (in this century).
My personal issue for BRINK is it's short campaign,the level 20 cap seems too short.
Forgive me if i have it all wrong,you are welcome to correct me of course.