Alright after playing around with Mega Man some I thought I would share my thoughts (for those of you who arent on Smashboards. This is all pretty much there too. Seriously, get a Smashboards acc)
Alright, so, Mega Man. First thing I noticed about him is his Blaster. The range on this thing is just terrible, and often does minimal damage that you shouldn't consider using it. In the air you have better options such as the Fair or Bair, and Mega Man is a sitting duck when he's stationary. However, it is decent to get a percent or two as you're running, but when using them while running as your F Tilt, you cant dash, and even then, Mega Man's Dash Attack is really good for combo starting. So really, his main projectile isnt too good. The Metal Blade (Neutral B) however is decent for adding some pressure and long range damage. Additionlly, the Crash Bomb (Side B) is great for adding pressure and causing your opponent to Spot Dodge, Air Dodge, or move, allowing for some great punishment, and if it connects, then its great for combobreaking/starting. The Lead Shield (Down B) is nothing to right home about, but its good for stopping projectiles and inflicting some hitstun to take advantage of with a grab.
Mega Man's Up Smash, Down Smash, and F Smash all are decent kill options. The Up Smash is great for a D Throw combo at low percentage and reminds me of Marth's but with a larger hitbox. The Down Smash is decent for edgeguarding and Fair -> DTilt -> D Smash combos, I've found. And Finally, the F Smash is the best out of his Smash Attacks. Its a charge shot thats nice for punishing landing lag and missed grabs. However, all of these moves have a huge problem: Lag. They all have a fair amount of start-up lag, especially the Down Smash, making them somewhat easy to be shielded on. Also, they each have huge end lag, especially the F Smash. Still, the F Smash seems to be excellent for edgeguarding, especially given the new Edgeguard mechanics.
Now to the aerials. Mega Man's Fair and Bair are quick slashes, both being great for comboing, especially the Fair. The Bair also carries decent knock back with it. The Nair is the blaster, which I covered earlier, and the Dair is a Meteor Smash. However, the Dair has insane startup lag, landing lag, and ending lag, as well as a small hitbox, so I don't expect that to be used much. However, I did notice something huge about it. When Mega Man uses his Dair, all his horizontal momentum stays constant, while his vertical motion stops. His Dair is very good for horizontal recovery, basically. His Up Air is a Tornado Blast thing (Think Air Man from MM2). Its got low startup lag and has amazing hitstun. One combo I was fond of was Uptilt (Mega Man Upper) into the Up Air. The high vertical knock back of the Up tilit when combined with the Up Air took characters very far. However, I haven't tested this with a human so I don't know how DI dependent this is, but at high percentages I found Up Tilt -> Up Air to be very good at taking lighter characters to the top blast zone. For comparison, this combo took a ~95%
Villager to the top of Battlefield.
http://smashboards.com/threads/smash-4-weight-rankings.367479/ According to that, Villager is mid-weight.
One final thing, I want to touch on Rush (Up B). Rush takes Mega Man very far vertically, and when combined with the Dair's horizontal recovery power, Mega Man has no issues getting back to the stage. Also Rush can combobreak (confirmed to be in the JPN release) so there's that. Oh, and Mega Man can attack out of Rush too, so with that and the combobreaking capabilities, Rush is very important for Mega Man to escape punishment and retaliate.
Hope that helps for anyone interested in Mega Man. :]
EDIT: Oh and the throws. Up Throw has a lot of knockback, but idk if its a killthrow given how high blast zones are now. F Throw is alright for spacing, but Mega Man sorta sucks at spacing, so... and D Throw is great for comboing at low percentages.
The whole Dair thing with horizontal momentum is sorta hard to pull off on the 3DS, but its a technique I think is worth it given how fast Mega Man falls.