The main game is pretty fun but the lack of people on multiplayer is disappointing.
I liked the single player challenge mode just wish it had more variety mission wise.
The actual multiplayer side of the game has been disappointing. Too small a player pool for me to find a game reliably. The game modes are interesting but only if you can get into them.
The enemy AI on the highest setting along with the highest difficulty settings for ballistics and tactical aides makes the game challenging. The enemy ai on hard will waste you quickly if you screw up or waste a shot so learning to shoot accurately is a must.