Sonic Mania works great on there too! There's also a port of Sonic Robo Blast 2 that plays in stereoscopic 3D!
Half-Life plays okay, but struggles to maintain 60FPS and the loading screens (including the four during the opening tram ride) take 30 seconds each. Not what I'd call playable, but still, cool!
Performing the jailbreak takes about 15 minutes and comprehensive instructions for all 3DS models and firmware versions can be found at https://3ds.hacks.guide. All you need is the 3DS itself and any device with a browser and SD card reader. You can even use an Android phone! Jailbreaking is virtually risk-free, and once done, never needs to be done again -- the customized firmware can be updated from the 3DS itself. Jailbreaking your 3DS will not affect anything it can currently do -- all your themes, games, saves, and home menu layout will remain exactly as you left them. All it does is add a few new apps to your existing home menu for interacting with the jailbreak.
Other benefits the person above me did not mention include playing online after the server shutdown through Pretendo Network, being able to take screenshots during gameplay, streaming gameplay footage to a PC via Wi-Fi without needing to track down, buy, and solder in a 3DS capture card, removing the region lock to play Japanese/European exclusive games on an American handheld (or any other combination), create backups of your save games from cartridges or installed titles and restore the backup potentially to a different cartridge of the same game, copy games from cartridges onto your SD card as items on your home screen so you don't have to worry about losing the cartridges anymore, being able to load DS and GBA games from ROM files on the SD card and run them natively without emulation using the 3DS's built in backwards compatibility mode, installing the 3DS version of RetroArch for emulating game systems up to the N64/PS1, and installing mods for 3DS games. I've heard good things about the ORAS romhacks, plus there's a mod for MarioKart 7 called CTGP-7 that adds a bunch of new car parts and characters (I like playing as Sonic) and triples the number of tracks in the game. Some of the ones it adds are even good! Plus you can play them online with other people who have the mod!
Here are a few helpful links to 3DS apps you should install after you've finished following the guide (and browsed https://themeplaza.art for a community created home menu theme that suits you, or created your own using Usagi's Theme Editor):
openagbfirm -- run GBA ROMs using built in GBA compatibility mode