I just started catching up on all the Halo 4 news that has been spawned recently, but I’m really confused as to what is being offered in the multiplayer aspect. All I know, is that it seems to be straying pretty far from what I consider to be real classic Halo, with all the talk about kill streaks, ordnance drops, custom loadouts etc.
What I would like to know is what is Infinity Slayer exactly and is it going to be a seperate gametype kind of like Invasion was to Reach? And what is War Games? Lastly, are we still going to get our standard Rumble Pit, Team Slayer, BTB, Multi-Team, etc.?
Well, from what I have heard, is that War games is simply the new canonical name for matchmaking. Infinity slayer will be a seperate gametype from regular slayer (Check the halo 4 section, then select gametypes. Infinity slayer and regular slayer show up as different types).
Furthermore, the regular gametypes will most likely be there. I can’t offer a source, but I think I heard that they wanted to enhance the regular gametypes in a certain way.
Anyways, this is just what I have heard.
EDIT: Plus I have heard that a classic playlist will be implemented as well. Whether this will be Reach-classic or actual-classic is still to be seen.
Infinity Slayer could possibly be separate like Invasion but nothing has been confirmed yet.
Infinity Slayer is the same as every other playlists, except the classic playlists, but it has ordnance drops or as you like to call it, killstreaks. I’d prefer to call it pointstreaks. 
I heard there was a new game type in development from the new bulletin.