Final Fantasy Tactics. I played it at a friends request on PSOne, and generally liked the gameplay. Then a few levels in it started getting HARD. I'd have to grind monsters in between every level, I didn't feel like my characters were progressing very fast, so I didn't seem to have many customization options, and the story was so poorly translated that I couldn't follow it. I dropped it after maybe the Dorter Slums level.
Then I tried the PSP update (mostly because the art design for the new cutscenes was so damn beautiful), and couldn't put it down. I read up on the game mechanics, and before long I had a superfast archer that could SHOOT POTIONS, an armored monk that was basically Goku, and a time mage/healer with a rifle.