Bit of a Mega post but just making it to outline to people still confused everything that is in this Halo collection.
Halo CE:Anniversary Campaign. (2 player co-op)
CE:A Old to New Graphics Switching
Halo CE (XBOX 1) Multiplayer in 1080p 60fps (No graphic changes)
Halo CE + PC Maps
Halo 2 Anniversary Campaign (2 player co-op) completely redone graphics for the campaign, new intro and outro cutscnes, cutscenes replaced with high quality CGI by Blur Studios, Graphic switch feature, New skull(s)?
Halo 2 Multiplayer 1080p 60fps (No graphic changes, possibly superjumping broke)
Halo 2 +DLC* + Halo 2 Vista Maps
Halo 3 Campaign 1080p 60fps 4 Player co-op (no graphic changes)
Halo 3 Multiplayer with Forge and Theater intact 1080p 60fps (no graphic changes)
Halo 3 Maps + DLC
Halo 4 Campaign 1080p 60fps 4 Player Co-op (no graphic changes)
Halo 4 Multiplayer 1080p 60fps + Theater, Forge, Spartan Ops (no graphic changes)
Halo 4 Maps + DLC
NEW HALO Xbox One MULTIPLAYER 1080p 60fps
New engine based on amalgamation of the past engines features, Looks like Halo 4 with Halo 2 features, weapons visible on player bodies. Spartans and Elites playable. Halo 2 weapons.
Forge
6 Halo 2 maps completely redone in this Xbox One Engine
Halo 5 Beta.
More info needed
Multiplayer playlists will have gametypes and maps from all 5 Multiplayer titles as voting options. Playlists for specific games will be possible. Campaign playlists will allow players to play things like "every warthog mission from Halo 1-4 one after another" or start at Halo 1 Mission 1 and Play all the way to Halo 4 Final Mission.
Everything unlocked by default, Skulls selectable for every title.