Even though Skyrim is an amazing game, my heart still belongs to oblivion and chances are always will.
Here are my PERSONAL thoughts on the subject
Main quest: Oh no , Patrick Stewart is dead! we have to find his long lost son and start gathering artifacts to stop a malevolent god, without going too much into it, the main quest is a bit of fun, probably about 8-9 hours of game play in this if you are speeding through the main quest.While not dragons, it is a jolly old romp through the plane of obivion.
7/10
Side quests: Here for me Oblivion really comes into it's own, the quests in oblivion are absolutely huge, I spent a good 14-15 hours plowing through each individual guild. You definitely won't be starved of something to do in oblivion. From the arena to the mages guild by way of the dark brotherhood. Theres a guild for every type of player.
10/10
Combat:....is ok, Skyrim has it pegged here, definitely not as fluid.
Enemies level up with you, so in theory if you so wish, you could in fact take on the main quest and defeat a level 1 god
or wait a little while and get your arse handed to you. Your call.
7/10
Conclusion
Definitely playable, however don't go into it with skyrim based expectations, treat it as it's own game with the respect it deserves and you will have an absolute field day, trust me.
Sherlock