If you like games like Monster Hunter, you'd probably like ... well, at least you might like PSO 2. Original MH was inspired by original Phantasy Star Online (as was Destiny, I really think.) PSO2 is a lot more actiony than the first, but I think I still prefer some things about it more than the current gen game.
I actually started with the very first one, for Master System. It's one of the games that got me deep into dungeon crawlers.
Open worlds though, I play ... a lot of TES. It's also one of my fave series, but one that isn't nearly as good without the mods to me? Not because I can't play without them (beyond bug fixes, like, wow) necessarily, but just ... the community is/was great, and just adds so much replay value or things like Ordinator which really change gameplay. Beyond that though, I like the cosmology and it's probably one of the few series I can really say I'm a real nerd level fan of. XD