So reading the announcement that MS will release an update that will allow you to play 360 games I’m wondering…
If you have halo 4 already, does that mean you can play it online straight away and you’ll just join the 360 server as if you were playing on a 360?
How have games played back in the past in relation to online
From what I seen of Major Nelson’s overview, each game is going to run under emulation with some of the 360 UI. You pop in the disc, download something (full game or just an emulation profile like the OG Xbox) and then play. You should be connecting on to the same servers (where available) that the 360 uses. For games like Halo 2 that no longer have multiplayer, I’m not sure how Xbox Live is going to work for them. Have a feeling it won’t. But playing stuff like GTA 4 or 5, you should be jumping right in there with other 360 players but also have the ability to broadcast, record and screenshot your games which is pretty cool.
More into here 
So it sounds like games that are still running and have servers ill be fine if that’s the case. I did check out the list of games already launched. Curious though as to why they didn’t have any halo games there? They are pretty strong first party games after all. Only keen on halo 4, fingers crossed. PLUS will assume that the games will be as they were as in split screen multiplayer!