One of the criticisms I have of both games is that the late level enemies always ended up being damage sponges, I would have preferred it if rather than enemies becoming more resilient as you level that they became more numerous, so that at least you feel powerful. Of the gameplay an immersion breaker for me was that many NPC's lives seemed to consist of wandering around town gossiping with other residents rather than working, Oblivion's society just seemed non-existent. And somebody earlier mentioned that in Fallout characters tended to lurch forward, which made placing trophies around the house quite challenging, so I agree with that.
A little off subject, but I just really felt the need to point this out, because of the profound improvement it had on the Oblivion-Fallout-New Vegas gameplay evolution.
One of the reasons I love New Vegas is the interesting but simple solution to the issue I bolded. Damage threshold allows a naturalistic feel to advancement as opposed to giving the monster a million Hit Points, for example.
Giant Radscorpion in Fallout 3
HP:1,000 -> Unless you sneak attack critical it with the Combat shotgun, this eats all your ammo.
Giant Radscorpion in New Vegas.
HP:165 Damage Threshold:36. -> Now, instead of just being a damage sponge, the target is more strategy and equipment based, adding layers to the progression by making it important to actually upgrade from that 9mm. It could take 200 shotgun shells to kill this monster now, or it could take one well-aimed 45-70 round from stealth.
Also worth mentioning, is this system makes playing on "Very Hard" Extremely rewarding, making the game feel a lot more balanced and fast paced. one to ten good shots (Depending on target) will still kill almost every enemy except some of the legendary enemies, while roughly the same will take you down. The stakes and combat pace are high with every battle, and rather than seeing a conflict as "There goes all my ammo" I find myself looking forward to every encounter.
We've strayed off here....describing the settings and etc isn't game play. For oblivion game play, it was fluid. You pushed your anolog stick in one direction it'd go in that direction. In Fallout, you'd push forward, and you'd go somewhat straight but you would be sliding all over the place, never a Straight line. I also noticed when you are standing still, and push forward, you almost make a choppy jump forward...like 0-100 mph kinda thing. For Oblivion, it was smoother. No 0-100, or sliding all over the place. I also think your screen should bounce slightly to give you that feeling that you are walking and not floating. I hope I described this well enough and my moneys on Oblivion.
That's not gameplay at all, that's interface and control. Nothing to do with the actual mechanics part of the game, at least, not directly.