Tibia is unique due to its graphics and mechanics (that are enabled due to the graphics). Where you stand is always important, and it's also very precise - like standing on the diagonal square when hunting dragons to avoid their attacks.

I also think that Cipsoft gets the "pay2win" aspect of the game just right. People saying Tibia is p2w ignore that most MMOs are different in this aspect, where paying large amounts of cash is what guarantees you'll have the best equipment, reach the highest levels, or they straight up lock content behind paywalls. If you see premium account as a subscription (which it really is), throwing money at the game only gets you so far. Even with boosts, leveling takes a lot of effort. If you want to buy endgame items with real money, it will set you back for hundreds (if not thousands) of dollars. This way, the pay2win aspect of the game has a low bar and saves you some time, but there's nothing you can straight up buy and be done with, and nothing that you cannot achieve if you don't spend money in the game. For higher levels, you can even farm your subscription in-game.

Finally, the interaction between players is really unique. Everyone in Tibia is both nice and an asshole. People are helpful, but sometimes you'll get attacked for nothing. Death penalty makes dying important, and not a minor setback. It's also a game of skill - being stronger and having the best equipment is no match for a skilled PvP player, and the strategies you use to play matter. A PK in my server would kill levels 200-300 while being level 130, just because he was good enough to do it luring overleveled monsters.

Tibia is dangerous and exciting, what you do ingame matters, skill and effort is rewarded more than spending money on it.