MMLC featured remixed levels where you warp from one point to another in timed challenges. They're nice, but why couldn't we just speed run the stages like normal? Upon release, the game didn't include a rewind button like Disney Afternoon did. This feature is great for kids or helping noobs learn a level quicker (people are busier nowadays). And actually now that I think about it-- the rewind feature is also good for runners because it prevents them from having to restart from the beginning over and over again. I'm glad they added this to Nintendo Switch version, which has it's own problems with having to download the 2nd half of the collection separately, but whatever.
I've read some complaints about lag. The frame or two delay didn't affect me until I tried performing the glitch-zip in Mega Man 1. This is an advanced trick that runners and enthusiasts use to warp through walls. You can perform this technique to skip sections and pick up the Magnet Beam before defeating Guts Man. I found it more difficult to perform on Legacy Collection. I also wished they took the time to actually remaster the games so they don't fall into slo-mo, and perhaps even add the ability to change weapons using the triggers. Mega Man 3 suffers from the worst slow down when too many sprites appear, and it would have been cool to re-experience these games without dicking through menus like it's 1989.
Disney Afternoon Collection has an incredibly fun speedrun mode where you can watch other runners as you play along, and this should set the precedent going forward. The NES retro library in particular has so many great games that would only work nowadays if they allowed rewinding to learn the stages and included a friendly speedrun mode with online leaderboards.
They also fixed the music section. In MMLC, you could only listen to one song at a time. Disney Afternoon Collection let's the songs seamlessly transition as a playlist so you don't have to choose a song every 45 seconds. Still waiting for a patch.
Someone messaged me on Twitter the other month asking when I was going to continue doing my no-damage, buster-only series on Mega Man. I told him that I'm tired of shadowbanning and socials in general are a drag lately. But even if I did have the heart to continue, I wouldn't want do it on the Legacy Collection anymore, because it's not the definitive version.