[@OtomostheCrazy]
On my first time, the last thing I did was kill Paarthunax, mainly because I wanted to do some super cool Blades shit, but then I realized that Paarthunax was a cool dude, so I spared him on my second playthrough. Overall, I'd spare again.

I also did Dawnguard, mainly for the crossbow. The final crossbow was so good.

Thieves Guild, did you keep the Skeleton Key, or immediately put it back in the Twilight Sepulcher?