So, I just completed Mega Man 1, 2, and 3 for the first time. The only 2D Mega Man that I have experience with is Mega Man X. I used to rent it over and over when I was probably 5 or 6, and I loved it. So, basically, I thought I'd share my unique perspective on the 3 original games. I will probably edit this post after I complete 4, 5, and 6, and share my thoughts on those as well.
Firstly, I'd like to say that I enjoyed all 3 of these games immensely. They were challenging, yet, still very playable. I should also state that I used save states throughout each game. As a result, I have developed a great respect for the patience, and resilience, for those that completed this without the use of save states.
The first title, and most challenging of the 3 games, is also the weakest. What makes it so challenging, is the slippery nature of Mega Man. This makes it incredibly difficult to land your jumps. Quite often, I fell to spiky deaths feeling that I was cheated. This doesn't totally break the game. You gradually develop a better grasp of the platforming and, with the power of save states, can make it through (often by the skin of your teeth) feeling satisfied with your handiwork.
When you aren't slipping off of ledges, shooting enemies with your trusted Mega Buster is still a good time. Enemies and bosses are colorful, diverse, and fun to shoot. Furthermore, earning weapons and deciding which bosses to try them on still feels satisfying. Playing this when it came out probably felt like a revelation. When I discovered that the thunder beam was powerful against Ice Man, all I could think was "get shocked you frosty bastard". Perhaps this was a bit excessive, but the game's hard.
Then you meet the Yellow Devil. This terrifying, mustard monstrosity, brings a new level of hatred into your soul. Eventually, you can figure out his patterns and watch his health, slowly, diminish; however, without saving periodically throughout the match, I just might have given up.
With all of this in mind, I still think this game is worth playing. It gets a pass on a lot of things in my eyes, because it is the first in the series. A lot of what the series does well started here, and that is an impressive feat.
Mega Man 2
Many people claim that this is their favorite game, period. I can see why. What separates this game from the original, for me, is the tightness of movement that it brings to the table. Mega Man moves like he should move. Unlike many of the situations in the original, when you die in Mega Man 2, it is probably your fault.
On almost every other level, this game is superior to the first. Immediately, you are slapped in the face with colors that are vibrant, and catchy, well composed music. It all clicks together as you play to create an experience that feels whole.
The enemy and boss design has also improved. They are bigger, more colorful, and are funner to look at. Near the end of the game, there are a few bosses that amp of the creativity, providing great experiences as a result.
There is a noticeable lack of slow down when compared to the original and 3. For some reason, I found that the other 2 just had much more of this happening. This reason alone sways my vote, and makes Mega Man 2 the best playing game of the original 3. I like smooth, and if I can call Mega Man 2 anything, it would be smooth.
Mega Man 3
Mega Man 3 is a lot like 2... except, Mega Man 3 has a slide. The slide great. As some dastardly enemy leaps forward, seemingly about to crush your tiny blue body, no longer do you have to hop backwards to dodge the foul machine; instead, you can slide elegantly underneath, leaving a bewildered robot behind you. Styyylllle.
Mega Man 3 is also the longest game of the original 3 by quite a margin. All 8 of the robot masters from Mega Man 2 make an appearance, in addition to 8 new ones. Unfortunately, our returning robot friends weren't prepared for the slide.
The one issue that I have with this game, is the slow down. It seems like there is a lot more of it here, when compared to 2. I wish the slide was in a game as smooth as Mega Man 2, so that it may achieve its full, stylish, potential.
Finally, I feel that this game has the best difficulty of the 3. It can get quite challenging, but it never feels cheap. Mega Man 2, felt a bit too easy at times, which makes this game feel well balanced.
Both 2 and 3 are amazing games. If I had to choose one, it would have to be 2, strictly because of the lack of slow down.