4 words .... High resolution texture packs ....
Get them and a bunch of the other mods.... without the comunity add ons this game isn't so fun but after adding a few mods it is very fun and enjoyable.

I liked it, did the main quests for the mages guild, the warriors one, the thieves one and the main quest of the game, all with different characters. Also a bunch of random missions and sidequests. Never bothered with the assassins guild ones though. But once most of the story elements were depleted, I uninstalled it. I'll probably wait till i forget about the plot a bit to replay it again in a couple of years. After a while, most missions get repetitive and if you play a mage, you can really concoct some powerful one shot spells. I think the warrior has it the hardest and the Thief has it the slowest (due to sneaking).

Sigh. I'd pay good money to have a program that lets me punch people over the Internet

Problem is someone else would have the copy before you and your counter punch would be late. ;)
On topic though, I liked it because it was new and was the first RPG I had played with a first-person point of view. I found the physics interesting and the open world nature really inviting.
After I found out about all of the mods I went mod crazy. Just because I could, I avoided doing the main quest and instead just explored and did the Mage quests, and then started on the Warrior quests.
Unfortunately though once you apply too many mods, level up too high and you're able to take swarms of guards, you loose a sense of danger. Sort of what happens when you apply cheat codes before beating a game for the first time.
It becomes, "Meh".
I found the Oblivion area (only been in a few) to be really interesting and took dozens of screen shots my first time in.
I have to admit that I haven' t played it since I picked up The Witcher last year, but I'll eventually pick it back up to at least finish the main quest.
All in all it was a game with a lot of potential, but it seems that they just made some bad choices (auto leveling definitely being one of them).

It's a nice sandbox, and you can make it a very pretty sandbox with a couple of graphical mods.
Aside from that, it's rather dull just on it's own. Add gameplay mods and it's passable.
I did start playing it again though, because I'm determined to finish off the main quest, which I've not done since I started a year ago, I just tend to get bored and return to Daggerfall or Morrowind if I want to game in the TES universe.

The game is fun when you add a lot of fan based mods . I reinstalled it recently put in as many mods i could find now its great playing some of the fan based content such as lost spires etc. Think now is the time to play it.

It is a great game.
Bad RPG, but a really great game.I played it for about 96 hours and loved every second of it.

A mod I'd highly recommend with regards to this is Kobu's Character Advancement System. It allows you to just play the game without having to worry about either powergaming to get the 5x multipliers or ending up with a gimped character, and also has enough options so that it can be tuned to just about any preferences you have. Combined with the more static world of Oscuro's Oblivion Overhaul it makes for a far superior gaming experience.

Of all the ways they could have improved on Morrowind for the sequel, it baffles me that trashing the idiotic and arcane levelup system wasn't on the list. I used a similar mod in Morrowind, and it made the game a lot more enjoyable and relaxing. It's good to know there's one for Oblivion as well.
Oblivion is not something I've played. I thought Morrowind was okay, but I tend to get tired of it after a little while. Daggerfall I didn't like... it was just a big empty box with sticky walls and irritating music. I'll probably pick up Oblivion once i can get the complete collection for $10.

I found it to be a great game, it takes a while to get into it though.

Morrowind is better than this hack and slash.

It was a great game....for the first hour, then just meh.
That pathethic story has disgusted me.

The previous games are all better than it.
I clocked quite a few hours in Oblivion, but a lot of the time I got frustrated with it. They had so much potential, I feel cheated with what the final product is. Just looking at a few of the better side quests makes you realise the potential depth they could have brought to the game. I'd rant about their changes in lore too, but the series never had much internal consistency.
For me:
Arena - Great hack-n-slash, the random loots especially. Makes for a fun if shallow experience.
Daggerfall - Great additions to what they started with Arena, and truly amazing in its day. Slightly dated now, but if patched up properly it's still a good game. Very much a sandbox, they pushed the limits of what they and the technology was capable of at the time.
Morrowind - More plot driven, and benefits from this. The seamless 3D world was great to explore. It had its flaws, introduced easy modding which could greatly improve the game. It may have cut out some of the things that were present in Daggerfall, but still was very good.

Oblivion I like it. (To an extent.)
Morrowind is still the best one ever. But Shivering Isles was so much fun.