Truly a great love letter to old school gaming. I quite enjoyed my time with it, with the difficulty mostly being fair with occasional spikes. The music was also pretty great too. The level design was also pretty top notch, with the stages being nice interconnected sections where you often find the boss door before the keycard you need to get in, and thus needing to find the keycard elsewhere. There's a minimap too, which helps. Every stage has either a health or weapon upgrade hidden somewhere too, and the paths to those are marked with a unique color on the minimap. Some seemed cheap to get, but still rewarding to seek out.

I've seen other concerns regarding the penultimate stage being too long, and I would agree since it's a giant sprawling complex where you have to find 9 specific spots for story reasons, and progress being lost on game over, but as the level is fairly generous with extra lives that does balance it out. Also when you game over and restart, what is kept is your map progress so you can find where those are again if you located them before running out of lives.

My biggest issue is the final boss, as there is a mechanic that in retrospect makes sense but I didn't think about on my first attempts resulting in a lot of deaths. However, knowing this mechanic (after the main dev told me it) made the boss more bearable. Still hard but since it's the final boss I can live with that.

I recommend this game if you like retro-styled games and great soundtracks because this really is a love letter to NES era Nintendo hard games without being nearly as hard.