Tales of Symphonia. I had just gotten into Tethe'alla, and was making a push to get to and beat Pronyma in one go, which was harder than i thought, because i had no idea what to do after they said "Colette needs a key-crest. Let's go look for one!" Ran around for a while before i caved and went to GameFaqs, and found it, then beat Pronyma, and was endlessly confused by the plot revelations revealed therein.
Monster Hunter: pissing me off since 2010.