Eh, I just have a sick obsession with killing absolutely everything. Once I completed my missing assemblies(Cybernano and *B*FG) and finished my Cyberdemon kills(I was missing mere single digit kills), I should have just stairdived the rest of it, but I felt compelled to finish what I'd begun, so it took alot longer then it needed to have done.
I'm a bit disappointed in the build I chose - I had heard good things about SS, and to be fair it was an effective method for a (very small) phase of the game, but a single pistol, no matter how accurate and powerful, isn't really cut out for killing twenty thousand demons. Most of the game was bladework with the Butcher's Cleaver, but unfortunately I had almost maxed my level by the time I decided that, so I'm lacking several levels between Fin, HR, and Bru that would have made a melee run significantly smoother.
Regardless, it was still pretty effective - I completed the first *B*FNG(N1) somewhere around level 200, and after that I ran around with the big gun up and the Cleaver on juggle, blasting away whenever it charged and chopping everything else to pieces. The only trouble I really had was Nightmare Arachnotron caves, which are a pain for almost any build - otherwise the 8 points of permanent armor I had kept damage on me to a minimum even while carelessly charging around amongst packs of mancubi and viles.
Once I finished the second big gun, though... let's just say the last 50 floors didn't hold up very well. Two of those things on swap with the nano pack on top of the nuclear charging clear floors absurdly quickly, and only a handful of enemies(Cyberdemons, Nightmare Viles, Shamblers, Lava Elementals, and Agony Elementals) can survive a single blast, much less two. Really the only trouble was hardened wall levels, because otherwise the initial blast not only kills everything in sight, but also exposes everything else by obliterating all of the walls in the blast radius.
As much of a grind as this was, the end sure was a lot of fun - not often you get to play with BFGs as your permanent primary weapon system. As a space marine, this is as close as you can get to calling supporting fire from an orbiting battlecruiser.