Going by reviews and threads here, it seems like most people (aka, the average person) is beating it in under 10 hours. If you don't care about the combat system and thus don't fight every single enemy in your way you can easily go into every house, talk to every NPC and do all their little quests for fruits, find most of the hidden areas like treasure cave, and blow through all the story dungeons in under 10 hours.
It's definitely a short game. I mean it really only has intro -> 3 stages/temples and then endgame and its not like the temples were particularly long either. Most were one or two giant areas with a bunch of puzzles/platforming/fights to get from the start to the end.
That said it's still a fun little game for the 2-3 days it lasts.