(Note: this is from the PSX version!)
This game, back in the PSX days, basically took all of what made THPS1 good, and improved it. With the addition of Manuals (Which were planned for the first game, but cut for time), Combos got longer, and balance meters were added too. The Levels each had their own hidden spots and skate lines built in, and the game rewarded you for it.
Probably the biggest addition in THPS2 that's memorable is the Create-A-Skater system, alongside Create-A-Park. While taken for granted these days, back then, they were revolutionary.
All in all, this game proved that it could take everything THPS had and make it even better.