I maxed out all cities' populations.
This was the 4th or 5th time I've beaten it. I picked up the OST & Symphonic Suite released earlier this year (marking 30 years since the game's release), which put me in the mood to replay it. I last played through it about 10 years ago, and I remember it taking 2 to 3 times as long that time. Even with the lengthy periods between playthroughs, I guess I've gotten to where it's become extremely easy, as I only had a handful of deaths throughout, didn't fail at any of the action stages, and got through the ending boss rush in one try.
Along with F-Zero, this was the game that made me want an SNES -- I'd beaten both games at a friend's place before buying the console. I really like the mix of action-platforming and town-building, which is why I was extremely disappointed with its sequel. Even though it's become super easy to me, I won't knock down its rating because of that. It was a pretty good challenge the first time I played through it.
