I have tried one CM12.1 nightly. This was an unofficial build by Ccrazy_boy at XDA. It gave a breath of fresh air to Android L. After a few days, this happened.
All About L – Part 2 – The next part of our dive into CyanogenMod L, an update on 12.1 and releases. http://t.co/Jo53dHYv7Q
— CyanogenMod (@CyanogenMod) April 9, 2015
Other than icon animation, the UI is snappier and supposedly less memory leak. Some users reported better battery life. That is subjective till Google Play Services is fixed.
25 Apr 15 update
I have since gone through several nightlies. Some are good, some are not so good, eg 19 Apr introduces a new compression that caused Gapps to hiccup. If you are planning to try CM12.1, 23 and 24 Apr nightlies are good.
The not so good stuff. From the lockscreen, everything requires one extra slide. Incoming call from unknown caller, slide phone icon, slide to answer. Unlock phone, slide lock icon, enter pin. Luckily for the camera is a one stroke function.