Growing up watching The Angry Video Game Nerd I always thought games like these were the hardest and most unfair games to exist, but of course that was mostly a persona to make the game seem more hard than it really is.
Playing through the game as an adult and its clear where the developers intentions were. You must study the levels as you die time and time again until you figure out the solution the devs had in mind. Hard jump with an enemy covering your landing? Look around, chances are there is a jump attack power-up nearby. Stage boss have a lot of projectiles? Maybe there's a hidden weapon in the previous level that will help.
One thing that I really like about the game that's different from others around the same time are the way continues are handled. As far as I can tell they are unlimited and they don't even send you back very far at all. Feels very fair and feels very satisfying after conquering a boss that took a few tries to take on.
Movement feels very satisfying as for the most part your character is able to do what you would like him to do. Wall jumping back and forth feels very good and falling from a ledge doesn't send you straight to your doom (Looking at you Castlevania). They game feels the best when you know where the enemies are and you can beat the level without ever needing to stop, just hacking and slashing your way through your enemies.
Haven't quite beaten the game yet but I do intend to. Just need to take a break after attempting the 3rd Stage boss a few times.