megaman 1 is decent and short enough to be able to learn the level orders without needing to resort to guides and not waste your time.. seriously tho, Elec and Ice man can kill you in 3 hits and you won't know until you played through the entire stage. it acts like you can freely choose but lock shit like the magnet beam behind a specific order.
megaman 2 is overrated. fuck that block section in Heat Man's stage i hate how they stuck with this form of the boss rush instead of letting you refight a handful per stage like the first game. also starting the trend of how your fucked at the final boss if you don't have some super specific weapon the final boss can only take damage from since you probably wasted it on the boss rush right before it. and yes, whoever designed that boobeam trap boss can get a metal dildo shoved up their ass.
megaman 3's atmosphere is neat with all stages being on different planets. my favorite is Needleman with the meloncolic music with what seems to be an abandoned city, makes you wonder what happened to the inhabitants. doc robot stages sound neat but 2 shittier megaman 2 fights per stage gets old. wily fortress has 6 levels but 1/3 of them are just single rooms.
megaman 4 is mixed. like some of the levels but the robot master contact damage can downright fuck your run over, some feel like i suck, some feel cheap. i feel like these were done on purpose to force you to use the charge shot which i find annoying to use. one time in the water guy's stage i jumped into the transition to the next screen and face first into unavoidable shitoko fuck that skeleton joe section in Cossack's Citidel with the enemies that rape you into the death pit as soon as you try to jump over.
havent played 5 or 6 yet. i think my favorite is Megaman 3 so far. if Capcom weren't greedy liars and rushed out entries in like 3 months we could have truly amazing games.