Kula World on PS1, people following the end of the year Top 50 threads might have noticed because I always have it high up, but this is the best puzzle game ever made if you asked me.
Basic premise is simple; just reach the goal. You play as a beach-ball and you'll navigate a series of beams traversable on all sides to collect a couple of keys and bonus items before reaching a goal. The level design is unbelievably clever, and it's difficult too!