Huge improvement over fallout3
the huge improvements over fallout3 are the weapons and their modifications. in fallout3 weapons types and their damages wasn't quite balanced. in other words energy weapons in fallout 3 were highly powerful compared to other categories which makes the skills in game aren't quite equivalent. In falloutNV weapons from different type were quite balanced. you could easily find a powerful weapon.
another great thing is the companion system. you are no longer have to travel alone like fallout3. every companion has a special perk you gain after recruiting her/him. the only sad thing about the companion system is you can only have one at a time. the saddest issue there is there is lvl capp at 30 so no lvling after 30
the game is just great. if you like rpg with guns you should never miss falloutNV
about the technical issues of the game... of course i ran into some including not being able to shoot in 1st person view and got it fixed by reequipping the gun easy. and had some CTDs (crash to desktop) few lags in crowded areas but i guess its from my card