Oblivion was okay for a while, but it really wasn't deep enough to keep me into it. When I found an artifact in Morrowind, it was like "So yeah, the artifact might be in this area, but what do I know? Have fun". In Oblivion it was like "Okay, you're playing this on the 360, so you must not like to think. The artifact is right here. I'll mark it on your map. Right there, see it? Having trouble? Here, I'll add an arrow pointing at it on your compass so you won't get lost. If you want, I can take you there right now, just click on the mark." Even non-artifacts were fun to find. I found a daedric katana in a ruin, and it was great. Best ruin ever. It didn't even need fighting, the atmosphere was wonderful, and felt truly primordial.
Then of course is the brutal crippling of the magic system. Morrowind had so many different spell effects, and all of them could be placed on an item, and any item could do anything. I had a pair of pants that summoned Ancestor Spirits and an amulet that shot fireballs. Even if the combat wasn't very good, the sheer amount of stuff you could do was great, and it was challenging. Remember the psycho wood elf from Hell? The one that begs you for money and then lays the smackdown upon your sorry self if you don't give it to him? I trained for days to fight him, enchanted my equipment, and was so hopped up on Skooma I could've taken a bullet to the chest, and he still beat me like ten times. Oblivion had no challenge at all. The only way I had any challenge in the game is when Umbra broke thirty seconds into Sol Sanctum or whatever it was, generic tomb level, and had to fight Gloom Wraiths with an iron axe, and even then I didn't die once.(I'll give the Gloom Wraiths one thing, their howling is scary when you're not expecting it, I played that level at like 2 in the morning and my nerves were completely shot when I beat it) Plus, yeah, the graphics aren't that good, and they become hideous at long ranges. I remember when I looked upon the Imperial City for the first time, from the cliffs above it, it was like a big middle finger flipping me off, in the middle of a vast field of Green Play-dough. I'll take Morrowind, bad graphics and all, any day over Oblivion.
And don't even get me started on Bloom. If I wanted to burn my eyes, I'd look at the sun. Games look so much better without it.