This game is so huge that someone reviewing it could go on and on about what they did, and someone else who is playing Oblivion would ask, "Are we playing the same game?"
Graphically, the game is beautiful. While many gamers complained about the combat system in Morrowind, the combat engine has been completely redone for Oblivion. The combat system is most likely more involved than many people may realize.
Loading screens are a bit of a complaint. This, however, is NOT the fault of the designers, rather the fault of Microsoft for deciding to make 2 versions of the 360, a stripped version without a hard drive, and one with a hard drive. As huge as the game is, I give Bethesda a mulligan on that point.
While I am not entirely sure that this game is as open as Morrowind was, I am certain that it is a VERY open game. You can still pretty much do what you want to do. Myself, at the 50 hour point, which when you count how many times I got stupid and forgot to save when I should have, actually puts it closer to 60 or 65 hours, I have barely touched the main quest. Oh, and there are still TONS of things I want to do before I get back on the main quest.
If RPGs are your thing, Oblivion is your thing. If they aren't, Oblivion may well make them your thing.