Since RetroArch hit Steam I've been on a retro kick (I use the proper release with all cores, not Steam's limited version). Having a unified interface makes it much easier to dive in, even if it the UI isn't the best and it takes some setting up.
What has held my attention the most though, is the hacks and mods you can get.
Genesis Plus GX Wide and
BSNES-HD
These versions of the popular RetroArch emulation cores can enable a customisable number of additional columns. Some games support it better than others, and Sonic 1/2 need to be
patched. A favourite of mine in widescreen is Shinobi 3, especially when you enable the hidden 6 button mode. Throw on a nice shader that does transparency well, and you're sorted. If you own the Sega Classics collection on Steam, you already have the roms and can just scan the folder where they're kept. You can even go into the Steam Workshop for the game and download other "versions" of games. By versions I mean hundreds of different games uploaded as "mods" because they're just roms uploaded for anyone to download. That includes romhacks and full games.
Super Mario World Widescreen
Super Mario World (SNES) Widescreen Project. Contribute to VitorVilela7/wide-snes development by creating an account on GitHub.
github.com
This gets its own section because it's its own project, even though it uses BSNES-HD core to run. You can use different versions depending on your preferred ratio and if you want pixel stretching or not.
Super Mario Land 2 DX
Super Mario Land 2 DX is a color hack for Super Mario Land 2 in the same vein as Link’s Awakening
www.romhacking.net
A very good colouration hack, to make a GameBoy game a GameBoy Color game.
On the subject of romhacking.net, it also has a hack for Castlevania: Dawn of Sorrow to disable the annoying stylus requirement. How the game should have been all along. There's also a Symphony of the Night patch to make it full screen (plus a couple other things).
Patcher64+
Patcher64+ Tool. Contribute to Admentus64/Patcher64Plus-Tool development by creating an account on GitHub.
github.com
I said it in the Zelda thread, but this thing is so good. You can customise a patch for whichever supported game and have as many or as few changes as you like. Widescreen QoL changes, animation, gameplay, models, and so on.
Super Mario 64 Plus
The best way to play SM64 on PC. Tons of options including UI, QoL, beta moves, modern moves, difficulty/challenge/mirror modes. Trailer shows a lot:
Obviously for legal purposes I will state that you should be ripping your own roms from your own purchases