I was playing Killzone: Liberation today and it's quite a challenging game. I began to fantasize about how proud I would be once I beat the game. That thought made me think back on all my prior gaming victories and wonder which one was the biggest accomplishment.
I think for me it was probably beating Mega Man: Maverick Hunter X. When I was a kid I was as good at Mega Man games as I now am at remembering other people's birthdays, so it made me especially proud to beat it.
So what PSP game did you find the most challenging? Also, what PSP gaming achievement (winning a game or doing something amazing) are you most proud of?
[Update 1: Fixed formatting error.]