I dislike the new UI a lot.
There are two main problems:
One: The Global Cooldown causes ALL abilities to flash when it's up. This means all of your bars will flash white every 1.5 seconds.
Two: Using ANY ability causes all of your abilities to go grey and they don't fade back in until after the Global Cooldown is up. This is a huge problem when you're a class that spams abilities every second, such as a Jedi Sentinel. Basically, the abilities never light back up and are in a constant state of fading grey and flashing. Because of this, you can't tell what abilities are ready, whether or not you're in range, or if you have enough resources to use the ability.
I play a Sentinel and it is almost impossible to determine when abilities are off cooldown. During my hardmode raid last night, my entire UI was constantly greyed out or flashing, which made it impossible to determine which abilities could be activated.
I could not monitor Merciless Slash, Cauterize, Overload Saber and Zealous Strike properly. I basically had to guess when each was ready to use. The other raiding Sentinel in my guild was having the same issues.
And don't get me started on the flashing every 1.5 seconds...