Idk if Warframe counts as an MMO, but it's the closest thing to an MMO that I play.
The lore is really cool, though it's mostly for the people who care about it as it is really easy to skip/miss.
The community is mostly super friendly and a big part of the game (yk, trading in-game items for in-game currency, clans, etc...).
The PvE of Warframe imo is top notch, fluent movement, satisfying weapons, time or characters, abilities, strategies and weapons to choose from and reach one can be upgraded individually.
The PvP however... It exists and that's all I can say about it, it's kinda just bad and no one plays it.
Idk what RvR means lol.
Oh, and the game is completely free with no forced pay walls and it'll run on pretty much anything.
Though it's not perfect, it's a grind (yk it's a looter shooter) and there is an annoying mechanic of items taking a while to craft