Oblivion is a huge game with many places to explore and many paths for your character to go down. It's not a straight foward game, you don't have to do the main quest if you don't wanna, go join a guild, do some side quests, become a thief, there's too much to do in this game for me to list. Oblivion has a huge open world, and buildings and NPCs aren't just there to be obsticles, almost everything serves a purpose. Specific people will do specific things at different times of the day. You can go into almost any building you find, maybe to open some doors you'd need a key or something. But for most doors, if they're locked, you can try picking the lock. You can even pick up random things you see lieing around in a house. The physics could've used some more work because sometimes when I try running down stairs, I won't go down them, instead my guy will run foward too much and go off the stairs into mid air.
-Assassins creed also has a huge world to explore, but it doesn't feel as open as oblivion. But the cities are huge and fun to roam around in. The acrobatics are really fun to use, and the crowd interacts with you. The physics and all that are realistic, how if you bump into someone while sprinting, you and the guy can acctually fall over and then the guy could run away in fear, get up and say something like "Watch it!" or pick a fight with you. The combat system was also very well done, but buildings and people are just there. Buildings are used for climbing and acrobatics, but you can't go inside them, and the people just walk aroud the city aimlessly. But overall, Assassins creed is also a very fun game.
-Overall, I think they're both great games with ups and downs, I give them both 5/5.