What I like in a game, my playing style, etc:
- I'm a big fan of exploration. I LOVE to explore. I love the satisfaction of discovering a sweet lookout spot, an epic ruin, a hidden sword/piece of armor, or a new city that I've never explored before.
- Relating to the last point, I like a big map with lots of things to discover in it.
- I want to be afraid to explore somewhere.
- I'm not BIG on combat, but I still enjoy it. I prefer the player skill as apposed to the character skill.
- I enjoy playing thief/stealth classes as opposed to skillful warriors. I'd rather make money in alternate methods.
- I like customization and being able to have a variety of different combinations of class, weapons, armors, skills, magic, etc.
- I want to be able to do my own thing. I don't want the game to tell me what to do or set out my character's story for me.
- Healthy amount of factions to choose from.
- I like mounts (Oblivion obviously has them where as Morrowind doesn't)
- Not a big fan of reading, although I will obviously do it if it's important.
- Graphics need to be good. As I said, when I explore, I also enjoy finding places that are visually appealing.
-Both games have exploration; interesting locations, new ruins, etc. Oblivion has scaled loot, however, so you won't really be finding any hidden artifacts without mods. Likewise, you may also want a mod to tame Oblivion's compass, which tends to point out nearby areas of interest long before you can actually see them.
-Both have a "big map." There's some contention on this point, since while official numbers say Oblivion's is bigger, many people say it feels smaller. Whether it's because of view distance, terrain, walk speed, or whatever, it's something to keep in mind.
-Morrowind combat is character skill, Oblivion is character skill, but in function both have mostly the same combat: face enemy, click until dead. Many people complain about Morrowind's skill-based accuracy (you can miss an in-proximity target due to the skill vs agility calculation, whereas attacks will always hit in Oblivion. There's no animation or notice that you miss, just a "whiff"), but personally I find most of them to be exaggerated. With only about 50 in strength/agility/weapon skill, missing was never an issue for me.
-Both have things to steal. Morrowind has far more things of value laying around, to the point of imbalance; once you know where things are, you can extremely quickly steal yourself a suit of some of the most powerful items available, and have enough loot to afford anything you want. We're talking under-an-hour quickly. Oblivion leans toward the other extreme. There's not much of value to steal, and what you do grab can be a pain to pawn off to fences (the only sell limit in Morrowind is selling a stolen item back to its owner). Stealth doesn't work very well combat-wise in either game, as you need high skill to move anywhere near enemies, and attacks immediately reveals you.
-Class is relatively meaningless in TES games. All classes have access to all skills, differing only in how quickly they're increased. Characters tend to blur together in late game. Morrowind is a clear winner in this case for customization, as it has more skills, items, spells, and equipment slots for changing appearance.
-You can do your own thing in either game. Neither main quest forces you to participate, though a few of Oblivion's quests tend to have a tighter "grip" while you're in the middle of them, in the sense that you can't just walk away until it's done. Morrowind's quests don't really care, you can wander off at any time. This can be a pro or con for different people.
-Morrowind has a larger number of factions. People disagree on which game does them better, and I'll leave that argument to them.
-Like you said, Morrowind has no mounts, Oblivion has horses. It should be noted, though, that the horses aren't well liked, being kind of awkward to travel on and impossible to attack from the back of.
-Morrowind has limited voice-acting and more dialogue than Oblivion, so naturally, more reading there.
-For graphics it would probably be easiest to just image search screenshots or search for YouTube gameplay videos and see them for yourself. Oblivion has the obvious technical advantage, while some people still prefer Morrowind's graphical style.
What I dislike:
- LINEAR GAMEPLAY. Just let me do what I want.
- No reward in exploration.
- Small maps
- Limited customization
- Not feeling emotion when I play (such as fear, excitement, etc.)
- "Go deliver this, go deliver this back, go deliver this back, OK - kill 5 of these things"
- Generic RPG creatures, gameplay, quests, etc. (Don't like WoW).
- I don't want to be forced to be a melee character because the magic class is weak.
- Not being able to sell stolen goods.
- Poor graphics and views from high points on the map.
-Both are nonlinear. As mentioned before, though, some of Oblivion's quests tend to hold on to you until they're done.
-As was mentioned, Oblivion's item-scaling removes the point of exploration for some people, so you'll want mods for that.
-Both have mostly the same map structure; large, open overworld, loading screens into dungeons. Oblivion also has load zones separating cities from the overworld.
-Customization was mentioned above. Mods can give Oblivion more item variety, but can't change the fewer equipment slots.
-Which draws more emotional reactions to gameplay? Can't really help you on that one.
-Go back, go forth, go back, kill these, summarizes most quests in both.
-Haven't played WoW and can't compare, but a common complaint about Oblivion is its generic fantasy setting and creatures.
-Don't worry about weak magic. It tends to be overpowered in both games.
-In Morrowind, stolen goods can't be sold back to the original shopowner. In Oblivion, they must be sold to designated fences.
-Graphics already mentioned above.