Really isn't that hard. Besides the Yellow Devil the other tough section is the boss rush at the end (which you must beat with no energy refills). It's actually a more lenient game than Castlevania I and Ninja Gaiden. And even the Yellow Devil has the same pattern every time so it becomes more manageable if you memorize it (yeah, I've beaten it without the pause trick).
MM1 was a masterpiece of game design in 1987 and still good even if outmoded by the later ones. Now Megaman X5 blows (to be fair I haven't played X6 despite being able to for years but video reviews put me off). X7 is worth playing for a laugh but is really a waste of time.