I can already tell how annoying Top Spin is going to be (or how fun, if you’re playing as Mega Man). Unlike in Mega Man 3, it’s not necessary to be in the air to pull off the attack, which is primarily why its frustration potential is through the roof. To be honest, the move doesn’t look all that enjoyable for the Blue Bomber to have to execute, but if it works it works I suppose.
Despite simply causing Mega Man to spin in a circle, Top Spin appears to have horizontal knockback, and a decent amount of it. In Sakurai’s E3 demo (and shown in the above GIF), Mega Man performs the move on Mario, who is then sent flying to the left a fair distance. Assuming Mario’s damage was relatively low, Top Spin may actually result in a KO under the right circumstances.