Oblivion is probably my favorite RPG, which is no surprise. The best part of the game is the NPC action. Instead of dumb NPCs who love nothing more than standing around waiting for you to talk to/kill them, they have lives. Legion Patrol's acctually patrol, killing anything stupid enough to be hostile to them. The biggest (in my opinion) battle in the main quest has a large amount of NPC on NPC battling, which makes a lot more sense then "Since you're so awesome, you go in now, and if you die, we're all dead. Good luck!" Depending on your computer, you may have some problems, but I really didn't experience this. Unlike Morrowind, important npcs can't die unless if it's a scripted death.
Problems: Guilds are almost all quests. Once you're done with the quests, you don't have much to do besides the Guildmaster's duties (which aren't much). They should really add mini-quests such as Fighter's Guild Raids (where fighter's go kill some npc's in a dungeon) The Main Quest is not as fun as Morrowind. The main quest can be done in little under a week, and you really only need to be level 2 to complete it. I'm hoping that the Elder Scrolls will make some better final battles, because both Morrowind and Oblivion's were way too easy.
Overview: Oblivion is certainly not lacking in graphics, but without a better main quest or guilds, it really isn't replayable unless if you rush through the main quest (like I did).