All four original Halo campaigns from the main franchise, including Halo Combat Evolved, Halo 2, 3 and 4 can be played within the Halo Master Chief Collection. All games have had a makeover, although the most difference has been made to the Halo 2 campaign.
343 Industries are still slowly rolling out the matchmaking playlists for the Halo Master Chief Collection, and so far there have been a few issues - give it a week and everything should be running. From there, we may have to wait a couple months before all of the playlists and the entire ranking system is ready for play.
As well as providing forge mode to all of the Halo 2 online levels, 343 have thrown in a few blank canvas maps that can be used to build to your heart's content. The new forge has tons of new items, scenery objects and special triggers to give you the chance to make the biggest virtual rube goldberg machine in the world.
Halo 5 Beta
If the Halo Master Chief Collection isn't enough for you, then you may want to check out the Halo 5 Beta when it launches - this is an exclusive to those who pre-ordered Halo: MCC.