You know what I hate about Fallout 3? The lack of detail. Unique weapons look the same as their counterpart, you always hear the same voice twice, lack of drug dealers and rapists, lack of smuggling, lack of cities, lack of weapons, lack of tribes, etc.
New Vegas fixes this by adding different looks to unique weapons, there is much more voices you will never hear the same voice twice (usually), there are a stuffload of drug dealers and rapists (go hang around freeside you will hear women scream rape every 5 loving seconds), you have drug and alcohol smugglers, there is more weapons you can shake a stick at, clan factions, etc.
I honestly think Obsidian should continue working on Fallout 4 or at least work together with Bethesda on Fallout 4. If you think about it Bethesda's fallout 3 is a kid game compared to Fallout: New Vegas.