90+ hours into Oblivion, and I'm still having a fantastic time! I think I can offer some comparisons to Skyrim now. Below I'll include a list of things common to both games, and which game wins as far as which I liked better:
Oblivion vs. Skyrim
Environment: Skyrim - "You can't compare graphics! That's not fair!" I'm not comparing graphics, because that wouldn't be fair. But Skyrim is just so much more immersive. Unfortunately Oblivion feels very copy-pasted. The boring English countryside comprises the entirety of the landscape, and it's rather unexciting after awhile. Further, the dungeons are all exactly the same, which lends little in the way of exploring just for the sake of it. It's always fun to find little story tidbits, and cool items in the different dungeons and burial keeps, but the actual look and feel of it becomes boring.
Fighter's/Companion's Guild: Oblivion - The Fighter's Guild story line for Oblivion just felt more exciting than the Companion's Guild in Skyrim. Yes, you can turn into a Werewolf in Skyrim. But what did that ever do for you? You could only use it once a day, you couldn't change back at will, and it only lasted like a minute or two. Plus you had to equip everything again when you did revert back. It wasn't fun. Also, you never got anything out of finishing the Companion's Guild quest line. They also continued that unending fetch quest loop at the end so you never were able to actually "complete" the thing. At least in Oblivion you got rewards for sending the guildies out questing.
Thieve's Guild: Oblivion - Oblivion had a super fun story line for the Thieve's Guild! Skyrim's was alright. The whole Nightingale quest was fun or whatever. But there was so much fetch questing involved...it seriously became a chore. My husband actually kept a written spreadsheet for which quests he had finished in which cities, just so he didn't go crazy. I actually wanted to continue the Thieve's Guild quests in Oblivion. I blew through them all linearly...they were too much fun.
Mage's Guild: Skyrim - The Mage's Guild quest in Oblivion was fun, but I thought a lot more effort was put into the quest line in Skyrim. It was the first guild whose story line captivated me. Not to mention the fact that you couldn't even get in for awhile in Skyrim, having to get your magicka high enough just to cast that first atronach to prove oneself. I thought that was a nice, albeit small, touch.
The Dark Brotherhood: Oblivion - I have to give this to Oblivion, because I killed Astrid in Skyrim and wasn't able to join that guild. But I've heard Oblivion's is better, and I'm certainly enjoying it immensely. My favorite quest so far has been the "Whodunit?" very Clue-esque house party where you kill each of the guests one at a time in secret. Too much fun.
Main Quest: Skyrim - The story in Oblivion is interesting, but closing the gates over and over has become boring. I don't really care anymore, and I've only closed two. I don't relish closing another seven, or whatever it is. And in Skyrim I'm referring specifically to the quest line about Alduin. The Stormcloak/Imperial quest line, I couldn't care less about. But I thought the Alduin story, along with the Elder Scrolls and just the whole shebang, was fascinating and completely captivating. I remember daily awe progressing through all that.
Miscellaneous Quests: Tied - I thought both games did an excellent job of scattering miscellaneous quests around the landscape, many of which were a lot of fun. Hands down, though, "Lost to the Ages" will forever be my favorite miscellaneous quest. That's the quest about recovering the Atherium shards in the Dwemer ruins around Skyrim. Fantastic quest.
Inventory: Skyrim - Wow, the weight problem in Oblivion is just abysmally bad. Things just weigh too much! I thought Skyrim was bad, until I played Oblivion. Skyrim did just fine, and I simply complain too much. Oblivion is ridiculous. At this point in the game, I can carry 400 weight on my own strength. I also have the Morag Tong greaves, which add 100 weight. I also have the Gray Fox cowl, which adds 200 weight. I also have the spell to feather another 75 weight. And I have potions that feather another 100 weight. Altogether, that's 875 weight at one time. And yet! I cannot clear a single area (i.e. Dungeon or Burial Keep) without having to leave at least once to sell things. That is insanity! I've gotten so tired of it, I just leave everything lying around at this point unless I absolutely need the gold.
Transportation: Oblivion - The horse in Oblivion seems to have so much more value than in Skyrim. I ride my horse everywhere. I got so annoyed with the horses in Skyrim that I never rode one. They died far too easily, and unless you bought the horse, it would just wander off and disappear whenever you would dismount.
Combat: Skyrim - I have to give the combination of dual wielding, spells, shouts, etc. to Skyrim. Although being able to cast a spell and wield a sword at the same time in Oblivion almost makes me change my mind...
I could go on and on, but I'll stop here. Both games have their pros and cons, obviously, and both are amazing games. Personally I have to give the edge to Skyrim for its far superior immersive quality. Plus I played it first, and I will always love it more. But Oblivion is a fantastic game all the same.
"It's not about the legacy you leave, it's about the life you live." ~Mara Jade Skywalker