It's really hard to say, many of the people who've played it have on the "nostalgia goggles". I put about 200 hours into Skyrim, 500 into Oblivion, and close to 1,000 in Morrowind despite having it crash fairly regularly for the first 300 hours I kept loading it right back up (This was due to lack of a graphics card, not the game being buggy).
Morrowind I would consider the best in the Elder Scrolls in terms of the overall experience, but not in terms of gameplay for reasons already mentioned. At the time I recall mostly playing games like the Infinity Engine RPGs (Baldur's Gate, etc.) and more linear JRPGs and was astonished just by the fact that "OMG I can climb that mountain" or "OMG I can fly" or "OMG I don't drown instantly in water"... it was little aspects of that first moment of "breakout design" that really pulled me into the game, things that are old hat and taken for granted now. I recently tried playing Two Worlds and it's sequel and quickly got bored despite several of the same conventions being present. It's just hard to compare the game in a modern setting without nostalgia.
What I still find the most compelling in Morrowind is the story and atmosphere. Every single quest feels more in-depth and involving, even with the lack of radiant AI, plus there's SOOOOO much more of it. Each Elder Scrolls game ups the "scale" but also seems to lose it in some regards. Oblivion to me never felt larger than Morrowind, only partly due to your horrible slow walking in the early game, more-so due to the fact that EVERY SINGLE THING... Every rock and tree is handplaced, it all is with purpose and feels like it belongs, and without any kind of auto-compass or map fast travel you really feel like you're exploring these places, and you get a much greater sense of reward from it. In Oblivion you had the terrible level scaling issues that made all items you found or were rewarded adjusted to your level, where-as in Morrowind, you can find super powerful awesome items that could be miles far above whatever you have now. Even the factions were much better, instead of 4 you had like 14 (Fighters, Mages, Thieves, Assassin, 3 Great Houses, Imperial Legion, Temple, Cult, and 3 Vampire factions) all with insanely more quests than it's successors do.
Some people call the dialogue in Morrowind very boring and stiff and people repeat the same things (every NPC has a library of auto-topics based off their location, job, and faction affiliations) but personally I found the dialogue much much more interesting. One of the early questgivers in the game, Caius Cosades you can literally talk to him for like an hour of realtime.
I'm rambling and I know but while the majority of the action gameplay is nothing to write home about, if you can engross yourself in that world, the atmosphere is top-notch. I still recall the horrible chill that went down my spine when I first ventured into Red Mountain, no music, just the terrible wind ambience, knowing I was vastly underleveled and could be slaughtered by anything, slowly creeping up the mountain to hopefully just take a glimpse of the top, where I knew my eventual fate would lead me. You won't get that kind of experience in Oblivion or even Skyrim, you never truly feel in those games that you are in a situation for which you are in true and constant danger (and believe me I've tried in Skyrim by modding my dragons harder and fighting armies of bandits simultaneously) it just doesn't compare.
