I've only played a little bit of Fallout 2, but never enough to really make a judgment call on how Fallout 3 is in comparison.
Even so, I have trouble getting into Fallout 3 because it feels like they don't do enough with what they could. I'm only at the Galaxy News Radio mission, about to get the dish from the museum, and so far most of the areas I've had to go through are all subway tunnels. The first couple I searched extensively, but after finding little in the way of loot or variety, I've found myself tired of subway tunnels and mostly head right for the objective. Exploration doesn't feel worth my time anymore.
Similarly, when I've been wandering the wastes, I've found the random monsters that attack me without purpose to be irritating. It was actually one of my beefs with Oblivion. I'm off exploring, and suddenly a random rodent is chomping at my ankles. Five minutes later, another little rodent is chomping at them. It is a bit irritating.
However, there are some encounters that I've really enjoyed and give the wasteland a depth of life for me. I was walking by a random ruin of a building, and all of a sudden there are gun shots heading my way. I wasn't in the condition to fight, so I ran away as best as I could. It was thrilling, and it felt real. I enjoyed the fight in the old grocery store for the Wasteland Survival Guide quest. I enjoyed emerging from the subway to get to the museum, only to pretty much hold off a siege against what felt like a dozen super mutants. I also liked it the first time I fought against a bandit barricade with mines littered before it. However, even that has been repeated and gets annoying once in a while.
As I said, I'm not very far in the game, but like Oblivion the game is so full of repetition that it is already becoming bland. I like quests, I like story and finding recordings for atmosphere, but I don't like being dragged through subway after subway.
If I was wandering the wastes, and all of a sudden I started to hear dogs/wolves howl and five minutes later had to fend off a pack of them and then having no combat for a while, that would be more fun than having to fight a single mongrel or rodent every five minutes. Even having some of the beasts vary their behavior would be a great idea, having some that won't attack unless you get too close, but even then won't fight to the death unless you attack them.
I'm sure the Capital Wastelands are interesting, but it feels as if Bethesda just strung a bunch of pieces together to add game time and take up space instead of being genuinely interesting and unique. As such, while I enjoy it, I've found much more pleasure in playing Mirror's Edge, Left 4 Dead and replaying Gears 2 with my brother the past few weeks than playing Fallout 3.
Quite interesting for what is commonly being called Game of the Year.