I've been revisiting the MP side of Halo: The Master Chief Collection throughout yesterday and this morning, as 343 has rolled out server updates to improve the functionality of matchmaking and other aspects of online multiplayer. I didn't see significant improvements yesterday, but this morning things have certainly changed.
My first attempt at the Halo 2 Anniversary playlist resulted in a nearly 10 minute wait for matchmaking. But moving on to Team Slayer I was able to secure a couple of stable games, with only a 2 to 3 minute wait. I also joined a full Big Team Battle match. Switching back to Halo 2 Anniversary I was matched with a full group in 2 minutes, but that game suddenly concluded without an actual opportunity to play. I jumped in one more time, and was able to play through a full game without issue.
Clearly, things are improving. I'll continue to revisit the MP throughout the week and weekend, and then re-evaluate the final score come Monday.