Mega Man 4 was my first Mega Man game and possibly even my first video game. My grandma had a nintendo with four games. SMB w/ Duck Hunt, SMB3, Contra, and Mega Man 4. MM4 and Contra were my favorites to play, and I even figured out that bosses had weaknesses and their order when I was like 4 or 5. I was actually surprisingly decent at Mega Man games even at a young age. When I was little I'd normally be able to play up until the first or second Wily Castle stage before it'd get too hard for me.
I remember my excitement when I found the wire upgrade by chance. I didn't even know about the balloon upgrade for a few years.