While Halo, the Master Chief Collection TECHNICALLY lies to its audience by including Halo: Reach and Halo 3: ODST under its umbrella, I don't think a single person will complain about this verbal "stretch."
The Master Chief Collection can be broken down into three simple parts: Campaign, Firefight(s), and Multiplayer. For those who are glued to the underappreciated storytelling aspect of Halo, make sure to check out the gorgeous campaigns or Halo 4: Spartan Ops. For those who love local co-op and taking on hordes and hordes of difficult enemies, Halo: Reach Firefight is likely for you. Finally, for those that love the classic, P v. P element of Halo, it is brought to you across six (!) lightning-quick and smooth Halo experiences. Moreover, you can customize which games you want to play in multiplayer mode. If you love Reach but hate Halo 2, you can uncheck the Halo 2 box before matchmaking. It is easy to navigate, fun to play, and nostalgic for all the right reasons (whiny 40-somethings screaming at you to let them take the sniper is concerning from a societal level, sure, but unabashedly delightful in practice).
Having gone away from Halo - and the Xbox in general - for a few years, returning to the game via the Master Chief collection was like jumping directly back into a childhood memory: Delightful, engrossing, and incredibly time-consuming (in a good way).
I cannot wait to continue to peel back the layers of this massive grab bag for months to come.