CyanogenMod is based off of android and is basically a mod. You can flash CM to your device if it is supported. Most devices are supported. CyanogenMod offers roms way after a device is discontinued.
CyanogenMod also has a lot of features that stock Android does not have.
Themes, Customization (lots), OverClocking (with a custom kernel as most Stock roms do not support), no bloatware, Speed, Root, and loads of other things.
I have been using CyanogenMod since 2012.
Should you use CyanogenMod?
CyanogenMod is great. It offers so many features that stock Android does not have. Those features are hard to live without. You do have to know what you are doing. I have ran into many problems (user’s fault). I soft bricked my Nook HD and had to put Android 4.4 (The only version of Android I could flash) on it :/. I got my Nexus 7 to not boot, and not be able to read the / directory. I had to rework some code to get it to startup :/. CyanogenMod nightlies are unstable. My Phone (HTC Evo 4G LTE) is stuck on Android 4.3. I really wish I put 4.4 on it when I had the chance. GPS does not work, 4G crashes my phone constantly, screen does not turn on sometimes, touch input does work, and a few other bugs. If you get a stable build of CM, it will be better than the stock rom on your device. I am not saying that nightlies are bad and not to use them. I have CM 11 on my Nook that is a nightly. It has no problems at all. My Nexus 7 2012 with CM12, has no problems at all. Bottom line, it’s up to you. I personally love CM. You should do more research in it if your are not sure. Beware, installing CM or any other rom, will void your warranty. If you are interested in installing CM for your device, there are lots of YouTube videos and forums to get you on CM. 🙂