I haven't played campaign a lot yet - waiting for a buddy of mine to get his copy and do co-op.
I have played a few hours of mercenaries, and wow. I don't know if brad was just trying to play it too much like gears, but I really like the quick shot feature, the camera while running, the feel of "oh shit oh shit oh shit" when running away from a group of enemies. Then again I have always loved mercenaries and I probably played the 3DS mercenaries more than any other 3DS game. Something about it is a addicting to me.
I guess I'm just not seeing the complaints that these guys had. Melee works fine, it actually rewards you for waiting for the right moment to attack by giving you invincibility for a moment. The laser sight aiming is kind of all over the place, but I also feel it rewards more controlled, burst shots. Mixing quick fire, running melee, and a finishing move together on enemies feels so GOOD.
I really hope people make up their own mind on this game, I understand why GB doesn't like it too much, but I think that if you can get past the learning curve (much of which you already have, if you've played RE4 or RE5) you will really have fun with this game.
If anybody wants to play mercenaries my 360 gamertag is JerBeep.