I never tried the pre-SP XP, but even SP1 wasn't too terrible compared to what it was competing against (there was a lot of perfectly-usable 95/98/ME still around with their lack of privilege separation, and 2K was mostly better only if comparing at the same amount of RAM but XP machines were newer and often had more).

For me, service packs were largely a question of "do we want to tie up the phone line for however many hours just because Microsoft wants to rearrange a UI layout?"