Adventure. Sun. Surf. Yo-Yo action. Definite fun.
The action part primarily consists of running through dungeon like caverns, killing wild animals, and supernatural enemies with a yo-yo, or spikey yo-yo-like objects.
Along the way there are puzzles to solve, secret paths to uncover, and tasks to accomplish for the various villagers you meet on your journey.
There are what I guess would be considered "boss" battles, however they do not up the skill level to any great degree. On average, I found the difficulty of the levels keep consistent. With the exception of a few challenging events, the levels mostly became longer then anything else. The final level did provide me with some frustration mind you.
Over-all, I found Star Tropics to be a fun, light, adventure!