@roipeker I hear you, we're in the process of re-doing all of our stuff in JS, moving from AS3. It has it's advantages, but there are disadvantages too. The whole ecosystem is definitely hard to wrap your head around coming from flash.
For pure animations, I think Spine is light years ahead of flash
We decided to use pure html/css for our UI. We had a custom UI in as3 with dropdowns, scrolling areas, buttons, list boxes, etc. and it was a HUGE undertaking. We really liked the idea of being able to get all that "for free" with html