I remember a time when MGR was unable to be purchased due to DRM issues. I'm unsure if that was an issue only in certain regions, I was only a console player back then. But it's good to see this game here and DRM-free, hopefully Konami will add the rest of the series onto GOG! Metal Gear Rising is almost nothing like the rest of the series in terms of gameplay, but the plot and characters fit into the universe fairly well (maybe turned up to 11 in some ways). The game has rock-solid gameplay (controller recommended), a phenomenal soundtrack, solid graphics (no native 1440p+ or >60 fps support unless GOG added them, but mods do exist), and a surprising amount of lore and worldbuilding via the in-game codec calls (over 6 hours of them!!!).
One of the best games of the 21st century, and maybe even onward. If you've never heard of this game, please do yourself a favor and do as little research as possible before playing it. It's absolutely worth going in blind and enjoying it your own way without any external influence. Grab the soundtrack once you've finished it, and go play DELTARUNE if you're craving more. Then grab those soundtracks too.