COD: Zombies is very fun to play with a friend with coop. I like to play it online, its a lot funner than single player
ULTRA SMOOTH, not a single lag ! The Online Multi-Player system is pretty impressive I'd say... or perhaps this is my first ever RTS Online Multi-Player game that I got hooked for quite awhile... Anyways, please make sure you fully completed the campaign mode and master the gameplay before heading over to the Online Multi-Player mode... You'll get trashed very badly at start... you need to train hard on different tactics and when you lose a game, LEARN how your opponent defeated you... it's really important... They have quite an active forum on their official game website, perhaps you can head on there to grab a few tips
Warfare Inc, very smooth online play. I tried my hand at it a while back (I've owned it for a long time but hadn't touched it for a while until the multiplayer update), and got destroyed. Didn't make it any less fun though.
I love how people think Eliminate is a rip-off. It's free, folks. You can't be ripped off for something that's free. It's your choice to download it. Anyway, even though you don't want to get COD just go for it. It's amazing and the multiplayer is extremely entertaining. Definitely worth the ten bones.