Installed CyanogenMod for my S4, my model finally got an unofficial ROM (i9505) so I thought I'd jump in and risk it. Installation was mostly trial and error because I'd never ever done anything this complicated as flashing a ROM before. Once I'd realized how to actually do the things they were asking me to do (All guides were telling me what to do, but not how to). Originally Wi-Fi didn't work on my phone (Other users reported anything from working completely, No wifi, to not working at all). Some kind soul on XDA gave me a terminal command to try, and Wi-Fi popped up right away. The only thing that currently doesn't work is NFC, but I've stopped using NFC so it wasn't a dealbreaker for me. Loving my S4 with all the UI lag completely gone. Sadly this ROM is unnofficial, unfinished and does not reclaim the space that Samsungs Touchwiz ROM originally took up, it's reserved by Samsung for updates, who knows though? A future CM update might clear that space out. It's nice to see my RAM usage sit around 500MB instead of 1.5/1.6GB. One little "quirk" is it doesn't display your carrier, it displays a number which represents it, if you look at the screen of my lockscreen, its displaying the code for my carrier (EE).