I beat Phantom Pain for the first time on Steam Deck because I was told the game was super long. I was shocked just how long it took me to beat the damn game (about 60 hours) and I cannot imagine people playing it on their home consoles back then as it's an extremely time consuming and laborious endeavor.
When they announced the Master Collection on PC I immediately pre-ordered it as I haven't played these games in a long time and wanted to have them on Steam Deck and to my horror, MGS2 and 3 didn't worked! Thankfully the community came up with some fixes that were easy to do and now all of them run nicely.
MGS1 is OKAY at best because they added an ugly bilinear filter that makes the image blurry and soft but my friends who are currently playing it don't seem to mind or notice so your tolerance may vary. IMO there are better ways to play MGS1 for sure but it's also the first time it's being released on Xbox and Nintendo.
MGS2 and 3 are the same as the HD Collection albeit with some fixes, eg the fonts have been fixed and the Codec calls loads faster than ever (something that always bugged me how slow the Codec was on my Xbox 360). Performance is a non-issue and better than ever with a rock solid 60fps at all times. I've tried the 2 MSX and NES games and they're fine while the bonus (new) music and books are great and can easily take hours of your time to read.
Overall I've seen a lot of vitriol about the collection and while I do agree it's unambitious, I think it's a decent way to play the series on modern consoles without having to dig up your old PS2/Xbox. To me playing MGS on the go in full 60fps is worth the price of admission.