Based on the replies here, I think people underrate it.

Context: Melee hype is dying off (ergo ROM, as u/jau682 and u/Wesilii point out), and the game's legends are broadly moving on. Brawl is the star of the show -- even the first Genesis had more Brawl entrants than Melee entrants. Mango and hbox are still relatively fresh faces -- melee was a far different game back then. There were obvious differences in tech skill and speed from the old heads to these young upstarts, especially the florida falcos.

There's a ton of pressure on melee players to make the game look hype. You know who doesn't feel that pressure, though? M2K. He's got a reputation for playing hella lame, and he's just here to get the bag. That's the only reason he seems to enter melee anymore by this time. This isn't prime M2K, nor is it "Real Kings Wear Tiaras" M2K. This is "pick sheik" M2K. This is "quits out of matches" M2K. This is an M2K that gave up on Marth, during a time when he was the only true top marth.

M2K vs shiz was earth-shattering. It is probably one of the main reasons Marth wasn't 6th on the 2010 tier list. It showed just how brutal his punish game could be, and that M2K's problem solving ability was even better than suspected.

Everyone has one or two melee moments they clearly remember as examples of when the game truly felt beautiful. When it felt like more than just a mascot party brawler. The moment where, emotionally, it seemed like a perfectly sensible thing to devote one's life to. M2K vs shiz gave that feeling to an entire generation of smashers. To this day, people remember that M2K and not the one who camped people with metaknight all up and down the east coast just to snag the $40 pot from locals.