Kirby's rival (and possible dad, don't ask) has been in the series since Brawl, and he hasn't changed much since then. I didn't realize he was supposed to have been the S-class tier character in Brawl, so much that tournaments didn't allow gamers to play as him, because the top players would be unstoppable. Apparently this wasn't true in Smash 4, and I don't think he's as godly this time in Ultimate.
Meta-Knight certainly is his own unique character. He's kind of light like Kirby, but his sword moves are much more fast and quick.
And he also has tornadoes and teleportation on his side rather than rocks and floating.
His Final Smash is Darkness Illusion, which is new and apparently based on Kirby Star Allies. He basically grows new wing and traps foes in a fury of sword swings. It's a decent final smash, but not my favorite.
When Kirby takes his power, he can summon the spinning tornado move. While some players are good with it, I don't find it as useful.
Online I did decent with Meta-Knight, but I could have been better. I found his jump recovery (like the other games) is rather terrible, especially as some moves can easily land you into a bottomless pit if you miss your target.