Mir is such a simple game in design, take the 1.3-1.4 etc they had barely any features.
my main guess would be that mir being our first real taste of mmorpg gaming, the world was very immersive, minutes would turn into hours and such. the graphics was of a good standard back then too, and the game play was unique.
sadly we have all grown up got jobs/real life commitments and our concepts on what is exceptable for an mmo has changed dramatically, most people want to play casually and playing casual does not work in a game such as mir. People who stick around playing mir waiting for that "ideal server" are chasing their tail, you will never recapture the early days of mir (euro / early private servers) its gone and the community with it, if you keep chasing that ideal server you will be left with a sore taste in your mouth and memory's of only crap, mir is not a solo game.
sadly wemade hasn't made any real effort to revive mir and bring it up to standards of the other competition out there, the cost of taking a risk on an mmorpg game these days is so big developers just stray away from being in competition with developers such as blizzard.
This is my opinion but id like to hear other peoples opinions on what made mir great