The singleplayer in this one really isn't that bad. Reuse of the same few multiplayer-oriented levels holds Order Missions (the bulk of the game) back but the fundamental mechanics are strong and the enemy design is probably the best the series has ever had. Soundtrack is excellent. Punchiest kinetic/explosive weapons in the series.
This is probably just me but the whole thing has a weird kind of liminal/dreamlike vibe, probably in part due to it being a long-dead multiplayer-oriented game.