Siege is nice, but only when you play with a group of friends. Its a very heavily team based, strategy and cooperation game. You can't rush in solo, you're more than likely going to die. You have to work with your squad closely, and I just can't seem to get that to happen when I play with randoms online.
And terrorist hunt, the AI are almost too human like. A terrorist with a shield will cover another one and they will move together, the one in the back popping up to take shots. Its incredible how good they can be sometimes, especially on realistic. Even with a squad of 5 and heavy planning, we couldn't do it. The bomber guys aren't that difficult, as long as you spot em fast enough.