So, this isn't some flame on Fallout 3, but here's the thing. I loved certain elements of it that New Vegas lacked, the rustic charms of a retro-futuristic 1950s Atomic Ara-esque America in a torn world, but then I remember all the BS Fallout 3 makes you put up, mainly those white scorpions and mutants from the Broken Steel, which conveniently meets the initials I used above. My point is though, I have a sort of nostalgia for Fallout 3, but between awful writing and there being nothing to do but kill things (Which bores me) and scavenge (Which is enjoyable depending on my mood), there isn't anything to do, whereas in New Vegas I'm ALWAYS finding something to do.

Anyone able to give me a good convincing reason to stick with another playthrough of Fallout 3?

I myself have played through the game over 10 times but still cannot give you a proper reason. You could try replaying on pc with mods for a much more different experience... i suppose.

If you need someone else to give you a reason to play a game because you don't feel like replaying it, you probably don't want to replay it and you shouldn't. Go find something new.

I actually much preferred Fallout 3 to New Vegas because in Vegas I never found anything to do. Fallout 3, to me, was always changing pace and going on with different quests and options. Sometimes to the point where I had so many, I didn't know where to start. New Vegas kind of throws you down an already set path. Wake up Goodsprings, check out Primm, head to Novac, head to the Airport, etc. It all goes in one line because the game was designed to throw you that way. You can of course head through Sloan and the northern parts of the map near Red Rock Canyon, but you will be slaughtered at a low level. Fallout 3 just threw you into the open world and had you look for shelter. The most convenient place being Megaton, but you could have taken residence in Springvale or the school if you wanted to. (I didn't see Megaton at first, since I came out of the Vault at night time. So I had to spend the night in Springvale until I found Megaton.)

Long story short, Fallout 3 felt a lot more open than Vegas. I agree that sometimes it feels like all you can do is kill things, but if you're like me and always find something with each playthrough, you don't get bored. I never went in Alexandra Arms, or thoroughly explored the SatCom arrays until my third or fourth playthrough. In Vegas, I had seen pretty much everything there was to see in one game.