My friend and I were playing, and the lag was awefull. It especially made driving the warthog difficult. I just wasn't sure if this was just lag from co-op only or just a low frame rate from bad performance all together. I haven't played by myself yet to find out.
My friend and I both experience really bad lag when we play 2 player co-op. Whoever is the 2nd person(not the host) is the only person who experiences it. We both have FiberOp 30Mbps internet service so it can't be a service issue.
We have played every Halo game co-op with each other and the lag has never been close to this bad...ever. There's definitely something wrong with the game for sure. I mean, I was experiencing almost a full second of delay between when I did something on the controller and saw it happen on the screen. No Halo game was ever that bad, we're not talking (ms) here, this is something seriously wrong. I don't even want to play it anymore until it's fixed because it's unplayable IMO.