I'm a total newcomer to Halo, and decided to pick the MCC before getting Halo 5, and I'm glad I made that decision. I'll review each game single player experience without taking into account they're dated games.
Halo: CE - It isn't a good game by 2016 at all, everything is so dated that the game is almost crippled. Yes, it's remastered, but the level design, the enemies, the missions, the dialogues and almost everything else is bland. Enemies are bullet sponges, the game has several difficulty spikes, and so on. It's worth to play through this game to get inside the Halo universe, but if you're up to fun gameplay, just play through the first mission, the rest is just repetition.
Halo 2 - When I've finished Halo: CE I was about to put down the series, but then I started playing Halo 2, it was a totally new experience, night and day really! Combat was tweaked so it became challenging and rewarding, there were new features in the game and the graphical overhaul was such that the game was almost on par with current gen. There are still some difficulty spikes, like the mission you are meant to get through 10 grenade launcher wielding overpowered enemies plus 4 hidden snipers which are able to down you with 2 shots. Even though the story, cutscenes, gameplay are very good and left me wanting to play more Halo. Which I've done going to the next installment.
Halo 3 - I was really getting into the series by this point, and Halo 3 didn't let me down. It isn't a gorgeous game because it's a port from the X360 rather than a remaster, but it's far from ugly or unfinished. The level design is very good, combat was tweaked once more, it's a blast to play through. At this point I was getting attached to the characters, and they were progressing just like my abilities to gun enemies down. In Halo 3 I've learned that no character in the series is standing still. Everyone has intentions and keep changing over time, just like real people. Halo 3 was the easiest one to finish, but it's far from easy, as you'll die several times through the game until you understand what went wrong.
Halo 4 - When I started it, I was becoming a Halo fan, and Halo 4 yelded the best shooting experience I've ever had on a console. The combat, as with Halo 2 and 3, was greatly improved. It's a staple in the series that the gameplay get a revamp over each iteration, and this one is a masterpiece! The visuals are so good that they're on par with current gen. The story and set pieces are very well crafted, the new weapons and enemies are cool, everything in this game is almost perfect. The campaign have a well balanced difficulty, and there are a few sections in which you'll die a couple of times, but nothing frustrating. Halo 4 has everything you could want from a FPS, and alone can justify the purchase of MCC if you're a newcomer just like me.
The campaigns altogether took me more than 40 hours, so yes you can bet it's worth my money!