There are quite a few subtle changes such as the follower's friendship wheel of which I've so far found 5, also they have gone more deeply into the tribes in this one, of which your rep is monitored individually throughout, there's power gangers(who hate my guts), Kings and The Legion to name but three. 

It's not just Brotherhood of Steel and enclave and raiders. I've come across a few Brotherhood of Steel corpses and the robot dog vet said he was in the enclave, this one seems to be about a main struggle of power between the New California Republic and Caesar's Legion (who they annoyingly pronounce "kaiser").

Other new things are further weapon mods and the ability to recycle your empty bullet casings on a reloading bench, to be fair the work benches in Fallout 3 bored me, so meh to that one, I'm playing hardcore. Also, you get hungry and tired and thirsty and bullets weigh you down - all fun new ideas. As for creatures there are a few new kinds of scorpion, giant lizards, giant mantis and annoying singing flying things, also plant men who are kinda like flowery ghouls also even in hardcore there seems to be less creatures about.  

As for Vegas itself, I popped in for a bit and it was ok but thus far I'd rather have been shooting up people than playing cards. If like RPGs with a Good sense of humour then it's well worth the caps! Sorry money. Oh and stealth super-mutant's called nightkin are pretty tough not to mention the massive death claw mothers!

Dedicated to trudy from good springs whose head got blown off in an ambush by the powered gangers.