I love how you gave each Robot Master their own personality! Top Man is goofy, Hard Man is imposing, Snake Man is twisted, etc. It gives them a lot of depth beyond just being boss robots.
My only complaint is that Hard Man being at the top, along with the absence of Dr. Wily, makes Hard Man look like the main villain. But that's a small nitpick.
All in all, you did a great job with this art piece! And yeah, I also have a soft spot for Mega Man 3. Not really sure why, but eh. Good game.