What is RDR and MP3 multi even like?
Well,
MP3 is easier to describe, as it's simpler: The MP3 single-player game is all about shoot-dodging. The multi- is also based on that core, but with various ways to customize your character, depending on the mission type and your desired play style. You can be a grunt, a sniper, a silent assassin, all with purchased items, which are limited by your in-game rank and the purchases you've made. I found it really compelling; much more so than the single-player, actually.
RDR is a weird beast. It's also similar to the single-player game, but there is SO MUCH TO DO in RDR single- that it's amazing they managed to convert much of it to a balanced multiplayer experience. There's no player customization other than your displayed Title and which avatar you choose, i.e. there are no skill or accuracy enhancing benefits. So everyone's on the same footing. You can do regular FFA and Team Deathmatch, or even go in a co-op mission with the various goals there. There're also capture the flag, progressive territory grab, and a snatch the gold modes, which are a blast, but nothing new. Later additions included things in Free Roam, such as holding onto a small patch of real estate, which alerts everyone in the server that you're challenging all comers. Those are exciting. You can also launch any of the game types from within a Free Roam. That's nice. Um, what else? Horse racing tournaments, all the single-player gambling modes are available as well... And basically all of the Challenges from SP also make an appearance in multiplayer, which is kind of a drag for the hunting and naturalist stuff.
The downside is, if your Free Roam server is unpopulated, it really makes the game's parameters glaringly apparent. The NPCs are few and far between, the realm feels dead without them.