What keeps me playing Morrowind, long after getting bored with Oblivion, are the hand-placed items scattered in the most unlikely places, the sheer number of places to find (some well concealed almost in plain view or just around a corner from a major path) and things to do (not all with the same character), the ability to do what you want at whatever pace you prefer and in many cases HOW to do them, the heavily intertwined relationship between the in-game books and the events that unfold around you, the sheer variety of different types of armor and clothing which you could wear simultaneously, the sense of satisfaction as your character goes from a pathetic weakling to becoming the most powerful thing in the game, and the ready ability to mod the game in so many fundamental ways.
Morrowind is a lot more tedious than Oblivion at first, since your character is nearly trhe weakest thing on the island, rather than having everything adjusted throughout the game to your character's level to maintain the same degree of "challenge" from start to finish. That's both a good and a bad thing, however, because on the one hand Morrowind's system leaves you with a clear sense of improvement over time, but on the other hand leaves you searching far and wide for any worthwhile challenges later in the game. The levelled and scaled opponents and loot in Oblivion, obviously a "solution" to the complaints about Morrowind's lack of late-game challenge, make the degree of difficulty relatively constant from day one, regardless of where you go or what you do. Venturing into "dangerous" areas in Morrowind at low level was suicide. Failure is not only possible at the start in MW, but inevitable until your skills and abilities improve, and you gradually become first proficient and then begin to excell at those things you work at. Overall, Oblivion was more entertaining from a combat standpoint, but never gave me the same feeling of satisfaction, since the blatant levelling and scaling made advancement relatively meaningless, aside from getting to see the next set of weapons and armor in the very limited and all-too-linear progression. High level items were present in MW from day one, although your starting character was unlikely to stumble across any right away, or survive whatever was in the way of them. Only the most powerful or wealthy adversaries carried the better gear, rather than have every passing bandit and thug carrying a fortune in exotic equipment late in the game. Ideally, something between them would be best, but each game has half of the answer.
The scenery in Oblivion was breath-taking in places, and I occasionally stopped my characters to just stare in amazement at the incredible view from some vantage point. The overall "artistic vision" was more limited, though, and it felt more "generic" overall, as opposed to MW's exotic and varied regions and denizens.
The animations in MW are just "primitive" in a lot of respects, and the game really needs the huge host of graphics mods that have grown up around it, as well as the unofficial bugfixes and code patch that resolve a number of significant but not fatal flaws. Modded, MW can look almost as good as OB in many respects, and better in some. Mods can turn Morrowind into just about anything you want, where the fully voiced NPCs and increased overall complexity in Oblivion make it more restrictive for modding, due to the inability to create additional dialog, although spoken dialog can be more "immersive" than a spoken greeeting followed by a block of on-screen text.
Ultimately, the decision is yours. Each game appeals to a slightly different market, and the occasional outbreaks of hostility on this forum between the MW and OB factions reflect the fundamental difference in the way that different people play the two games.