Some people have higher standards then others. I play a shit load of 3rd person shooters and I have played the game twice this year so it's failings are really standing out to me.
I think second playthroughs say a lot about a games quality.
I also played Spec Ops twice, got all the achievements.
Not saying it's gameplay was great, it definately has it flaws but I would probably call it average at worst. I guess I feel that the sum of a game can be greater than it's individual parts, and I'm willing to take average gameplay for granted if the game as a whole gives me a worthwhile experience.