That's the whole game.
Honestly, i really enjoyed it even back in the PS2 days with it's terrible frame rate but yeah this game is somewhat overrated because there is really not much else to do other than killing shiny lizards in the overworld for extra grip. The prestige this game got came mostly for being artistic and unique.
I'd say stop playing if you're not feeling the game.
Hmm, conflicting advice... I think I'll sleep on it :)