Since you're a Metroid fan I'll post this copypast I've made for you, hopefully it's helpful:
For Metroid Fans. This is a post I copy and paste but I hope it's helpful to someone interested in more Metroid. Fans have done alot and the series has possibly more great games because of it than anything beyond Mario.
I don't agree with the general sentiment that the first two games have aged that badly. The first 2 games certainly aren't as polished as the newer ones but I think they have some charm still. However fans have certainly made them better with Metroid HD being a terrific improvement hack and Metroid 2 EJRTQ being a quality hack that adds colour. I'd suggest that anyone play them like that. I'd also recommend all to play the two terrific fan games AM2R and Metroid Planets that remake the first two. AM2R has an excellent Reddit community continuing to evolve the game. Metroid Planets has a terrific remake AND reimagining of the first game that unlike Zero Mission stays faithful to the original mechanics. It's not well known but it's astonishingly well polished.
There's also a considerable amount of awesome mods/hacks on Metroid Construction, especially for Super. Super has the terrific mod Project Base that creates a more modern experience and Fusion has the quality Sequence Breaking mod that opens the game up. Aside from that there are all new experiences. Here's the best hacks that create all new games based on my experience. There's many others worth playing as well but this is a great start.
Over the Moon
Ancient Chozo (Similar to Super but different and gorgeous enough to recommend on it's own)
Nature (Vanilla, means it has little to no graphical or mechanical changes)
Retroid (Metroid 1 remake in the SM engine)
Y Faster (Speedrun)
Y Faster 2 (Speedrun)
Super Zero Mission (Hard)
Redesign Axeil Edition (Hard)
Cliffhanger Redux (Very Hard)
Scrolls 6 (Haven't played it, heard good things)
Also there are some real cool randomizers:
A Link to the Past and Super Metroid combo randomizer
Zelda 1 and Metroid 1 combo randomizer
Varia Randomizer for Super Metroid
Metroid 1 Randomizer
Zero Mission Randomizer
Fusion Randomizer (In Beta)
It's really quite amazing what fans have done for the series. Even the first two Prime games have randomizers. And despite what people may say even Other M is a decent game, albeit with a silly story and some clunky mechanics. Thankfully there's a mod for it too called Other M Maxximum Edition that fixes most of the common complaints.