The reason gamers would dislike SP2 would be related to the firewall, and possibly some security software.
Firewalls slow down network traffic -- not enough for internet browsers to notice, but not having one might give you an edge in a networked game.
Online games would make sense. However, the games we play would probably not overtax the local net (Age of Empires, Empire Earth, Rise of Nations).
Although his Athlon 1200 gets cranky slow from time-to-time since it's Win98 days.
I should quit talking about this. He's looking over at my boxes and licking his chops.
I used Win98 at home until I broke down about a year ago and got XP. On Win98, I had been experiencing ever increasing problems, crashes, hangs - and one most irritating, no shutdowns, necessitating a power off, and the half hour scandisk - because I didn't shutdown properly, LOL. I kept updating frequently in hopes to rid the OS of these problems. XP has been working fine on the same HW. My Win98 machine at work does not have problems - company does not permit updates from MS, only through their distribution.
On Win98, I used a winmodem for years, and typically got 56kb connections using Win98. With XP I could not get anything over 28kb. A computer support person at work told me I'd have to go with a modem with an internal DSP to get the speed back up. I did, and managed to get speed up to 48kb. XP definitely is a performance drag over Win98.