While the chances of getting a new Mega Man game seem to grow slimmer with each passing day, one thing is for certain, Mega Man is in the new Smash Bros. and he can hold his own against the other mascots. That's right, in a game with Mario, Sonic and Pac-Man, Mega Man is arguably the best of the bunch at this early point in time. There's still a long way to go until the game releases, and we're just talking about the mascots (not the dozens of other characters), but so far, Mega Man looks pretty good.
From a casual standpoint, Mega Man has a good Final Smash. He shoots a moderately large shot from his arm cannon, and when it explodes, it creates a much larger black hole-like object. Any characters sucked into the black hole basically take a KO. It's possible to survive Mega Man's Final Smash, but the chances are far less compared to some of the other Final Smash attacks in the game.
In a free-for-all battle against three other players, Mega Man can play a ranged game with his arm cannon, or move in close and use his down smash to really cause some damage. In fact, Mega Man's down smash is arguably one of his best attacks. It hits on both sides of him and will send higher damaged opponents flying to their doom. It can and likely will be punished by better players, but when used wisely, it can cause havoc on multiple opponents.
From a more competitive standpoint, Mega Man has a solid vertical recovery option, but not a lot to work with if you need horizontal movement. At the moment, it seems as though he's more of a ranged fighter compared to a character such as Little Mac, who must be close to an opponent to inflict damage. He feels a bit like Samus, but his unique attacks set him apart from most of the cast.
Defensively, the Leaf Shield works well in one-on-one matches, but isn't quite as effective in a free-for-all against multiple opponents. It allows Mega Man to unleash an attack or two, but it's best to use it as a wide projectile attack. It's not as fast as his normal arm cannon, but the larger size of the projectile makes up for the lack of speed, especially when playing against two or three other characters.
So far, Mega Man has a lot of attack options at close range and from a distance. His lack of horizontal recovery may hurt him in the long run, but so far, he can hold his own pretty well. He doesn't have the power of some of the other characters, but he makes up for it with decent agility and good ranged attacks.