Endless War games are awesome!
I know the enemies just walk to where they last saw you, but it really does have a feeling of them coming to look for you when your hiding behind a wall.
I like the team part aswell, telling your comrade where to go, it's good to surround the enemy. But mainly i often use my team mates for bait, get them to show up behind an enemy to turn him around, then i pop out from behind him and shoot his head off.
Some of the more 'epic' levels with 20 people really slows down, and it is distracting, but you finally understand what's happening when theres only like, you and 2 enemies left.
It has replayability too! you can easily go back and play the levels in loads of different ways. I'd really love to play more of these games.