I actually think MP is not that bad... it has its fair share of problems, namely the fact there is NO auto balance at all, and it only has a 12 person cap, but it's far, far from horrible.
I'd say it's simply average. The maps are well designed, but it seems as though Stopwatch and Objective are the same thing... except in Objective, the map is STRICTLY Allied vs Axis on one map.. on Stopwatch, it's two rounds, with each team having a turn as the Allied and the Axis. There is really no point that I can see in playing Objective, since it seems no one ever wants to be the Axis (whose role is always just defense, at least in what I played).
The classes are a little bland, and with only three of them, there isn't a lot of variety.. once you get the self healing aura on the Medic, he becomes a powerhouse.
There is no real point for the medic, because the respawn timer is incredibly short. By the time I get to someone to revive them, they have already respawned. In fact, the classes as a whole aren't really distinguishable from one another.. there is no real point to the Engineer in TDM, seeing as how the Medic and Soldier have the same (or better) weapons or better abilities.
The weapons are decent, no one weapon feels more overpowered than any of the others. You just pick a weapon in your loadout, and stick with that, but you can change weapons each time you die. Other than the Medic, the class specific veil powers aren't really that great.. the Solider's veil strike is so easy to avoid, and the engineer just has super speed but it is diminished so fast.
These are just a few detailed impressions I had on it.. imo, it's far from horrible, because it is playable and can be fun. It just feels like it needed more time, and that the biggest concentration on the game was on the SP. It's a fun diversion for right now, but I don't see this being a fixture in my MP gaming queue at all.
I haven't found any lag in the matches I've played, but to me, the #1 biggest problem is this game is that is no auto balancing.. one of the loading tips even says "It's polite to switch teams when you notice a difference in numbers" or something to that effect... but NO ONE switches. Why? Because there are achievements for being on the winning side on each map, so if you're outmanning them 6 to 2 in TDM of course you aren't going to switch, no one ever does. A frequent problem is that it's 6 vs 6 to begin with, 4 people on my side time out, and no one wants to switch sides.