Megaman is fairly mediocre, sadly.
His u-throw allows for great mixups. U-throw -> metal blade, punish their dodge or hit. His d-throw combos into a few things and can trick them into air dodging for a punish. If they don't waste their jump you can u-smash them and if they do waste their jump, you almost certainly get a u-smash.
Megaman can easily u-smash OoS against virtually anything and his grab is AMAZING. His throws not so much, but he can get those grabs.
In a few cases MM can d-smash OoS and kill as low at 90%! Unfortunately this is a very rare occurrence and is less "MM did something good" and more "they did something bad".
Megaman's bair is great off stage but useless on stage as it is near impossible to short hop it. Fair is nearly worthless on stage or off -- it racks up damage but that's it. There's no followups if they DI properly and it often leaves MM vulnerable. MM's u-air is a good pressure tool but is hard to hit with. His dair is awful.
MM's general strategy is "metal blade - > grab" and spacing nair/jab/f-tilt. Pivot jab is really good for tacking on % and making the opponent make a mistake. Crash Bomb forces the opponent to do "something" and gives MM an opportunity to punish.
Leaf shield is near worthless.
Z-dropped metal blade is an amazing approach. You can actually z-drop a metal blade
while in a combo and it hits the opponent for 5%. Pretty cool.
MM's d-tilt and u-tilt are okay, but situational.
Megaman has a guaranteed edgeguard, 0-death, against Link if he recovers to the ledge or goes below the stage (footstool or just bair off the ledge). Megaman's edgeguarding is super on point against some characters, non-existent against others. Footstool is king with Megaman.
MM's wall jump makes him hard to ledgeguard as you can wall jump -> bair from the ledge pretty easily. If you have the opportunity, leaf shield -> roll onto the stage is okay but you never get that opportunity.
MM's kill moves are d-smash, u-tilt, bair off stage, and u-smash, each being difficult to land. If MM's u-smash can kill you at around 100%, MM could be a nightmare. If it doesn't, he's probably not that hard to beat.
MM's biggest advantage is that unlike Mario, MM's options are constant throughout the entire stock. Mario is strong early on and then suddenly has to land the kill and, without a fireball approach, can't quite get it without a read.
MM can just keep doing metal blade combos and racking up % with crash bomb / metal blade / leaf shield / jab from a safe distance.
MM's jab is unpunishable if done right. You can walk forward and shoot 3 pellets and short hop backwards after the third and it's been unpunishable so far.
MM's d-smash hits you if you're on the ledge, but really only works if you don't have your invincibility. MM's d-smash isn't nearly as meaty as it looks. Kel has walked directly into the flames and punished me on more than one occasion.
MM can steal the ledge from you and then drop off -> jump -> bair, but it's not guaranteed.
All in all, MM is a character that a strong player can play and do okay with, but while someone like mario needs one good read to get a high % combo or KO move, MM needs like 3 or 4 in a row. Because so little is guaranteed, I don't see him doing particularly well in general.
THAT SAID, I believe Megaman will benefit greatly from moving stages and platforms. Playing on battlefield is a totally different ball game for Megaman, and his d-throw is suddenly an incredibly pressure tool.
If MM is stuck on FD, you can corner him really easily. On Battlefield he can be comfortable at any location.
Also, wavebounce metal blade is awesome. As is hitting it to the ledge, grabbing the ledge, then picking it up with an aerial.