Unpopular opinion: I dislike levels, and it's not for the act of going through the hoops of actually leveling.
I'd still want to do every quest and unlock my abilities over time, I just dislike levels as a measure of progress because of how removed from the world they are. The concept of exp and levels is so meta and purely for the benefit of visualizing player progress and gating content (which can usually be accomplished other ways); levels don't actually "exist" for characters... we train (learn abilities) and acquire equipment upgrades, but the power that something like "levels" provides just makes the problems of NPCs feel fake and insignificant once you get high enough. I'm supposed to believe these level 15 bandits are a real threat to the town but it takes me 20 seconds to clear their entire camp - it's so easy it's insulting that the player isn't always helping with everything . (I can hear Fray's teeth grinding at that, but I'll rest when I'm dead - negligence feels like an act of violence when you're this disproportionately powerful).
I know a more immersive world design would probably never work for an MMO today, players tend to favor the convenience of skipping mobs and the catharsis of tearing through older content, and I know I don't want to struggle through level 12 vultures just to pick some herbs any more than the next person, but it's still something that nags at me if I think too much about how fake/boring the player's strength is.
I'm just glad FATEs and dungeons tend to recognize this and scale us down to curb the power creep, so some of the world still feels as relevant as it's meant to be.
A more popular opinion: I wish there was more emphasis on communities.
So many MMOs have gravitated toward the convenience of automatic matchmaking, which is great for the solo player in a hurry, but it's kinda become a standard. I'd like to see more emphasis and encouragement for players to join more structured communities like FCs. "Alone together" is kinda what it feels like in a system like DF. Maybe some improvements to recruitment tools for FCs? I donno.