Even if there were no interesting quests or characters over the next hill in FO3 (which is very much a subjective matter and we're all going to have different opinions on that) the fact remains that there is still significantly more "next hill" to explore.
NV doesn't have random encounters and the map area is much smaller; regardless of what you may feel about characters and locations, FO3 unarguably has NV beat in sheer distance you can cover while exploring.
Like i said the map is zoomed out more, so it feels smaller. And even if the other one was bigger. It was just a rock here, a rock there, another rock there, a mole rat there, then eventally... a destryoed building there!
I would much rather good dialouge, good quest, and good story, over just random crap to make it so it takes you two hours to get to a hole in the ground were you will die. There were only a few characters that i really liked in fallout 3, not one companion did i like, except dogmeat.
Boone, Veronica, All 1st Recon, Colonel Boyde, and Hsu, Yes Man, etc. These were all some of my favorite people, now obviously i have more, but these are those who stand out.
The locations might not be "As Detailed" but they are more intresting. There are 40+ places that i found interesting, While in FO3, it felt like they just used the same buildings, and places over and over again. The only places i liked in FO3 was... Dunwich, Megaton, Tenpenny, Rivit, and... uhhh i don't know anymore, i guess the subways and the mall district.
o, and the random encounters only happen if you pick wild wastelander trait now, this is for the serious minded people who hated those weird things happening, so now its in a small package.
Now i know what i like about the exploration thing more then FO3. In FO3 some of the buildings/locations didn't feel like they fit. I would be walking in a completly no vegetation area... and right in the middle... a Giant oasis.... i was like WTF, it defenatly took away from emmersion. I don't explore much in this game tho, only if i want to get a weapon, so maybe your right.
My favorite activity is taking boone, and rex, then stocking on ammo for snipers, Get my Anti material Rifle, Mysterious Magnum, and E-Cluds C-Finder.
Then we head off to a Ceaser's Legion camp, Ussually that cotten woods place or whatever. Then i sit on the cliff and pick off Legion. It's great Target Practicing.
They freak out, but can't find me, so they run around wildly.
I just wish C-4 did not cost so much!!