Wow, such a game. The atmosphere is just amazing. It screams "mistery" at every screen. The scenarios are mesmerizing, and just watching the environment feels mesmerizing. I can´t emphasize how amazing and immersive the atmosphere and scenarios are, full of details, and able to ause a deep feeling of strangeness and alien-ess
The map design is really good, not only the aesthetic (wich is also suprb) but the layout and interconections.
Also happy is not a super-hard hack, and dosn´t need to abuse mechanics or use "special skills" as perfect walljumps or bombjumps (wich you can anyway use to your advantage)
My only complain is at certain boss, wich can be quite hard without a certain powerup you could or not have found by the time you reach it, and not being able to backtrack to gain power as the way back before that boss got blocked (and the save chamber is on the boss side, so if you play using save chambers you are forced to just fight the boss with no chance of going back) - Also when you beat that boss, it could be terribly annoying you can still get killed easily on the way back to another save chamber or being able to recover HP after the fight.
Played it on a original SNES (Pal version) using a flash cartridge, worked wonderfully. (And also forced me to use save chambers and no savestates or any emulator option)