A change went in with the last Wrath Beta patch that's deceptively simple, but may have far reaching ramifications for many of the classes in game: Both energy and mana regenerate on a per second basis, rather than the previous ticks. Instead of a chunk of mana or energy every few seconds, you'll now see a steady trickle reappearing constantly at your bar (outside of the 5 second rule for casters, of course). As a friend put it, "Woah. It feels like I am playing Diablo II now."
You can see an example of the change in action in the video above from Youtube user koblec.
The energy change should be especially helpful for Rogues and Feral Druids in that they won't have to obsessively time their attacks to the rhythm of the energy tick system, and should be able to use extra energy from talents in an easier and more fluid manner. Likewise, mana and energy users alike won't be waiting for that one last tick to cast a crucial spell or ability, but can cast as soon as they have the mana.
Plus, it's honestly sort of empowering to see the mana bar running up like it does. Technically, I'm not regenerating mana any faster, but watching that blue bar go up so quickly makes it feel like I am, and makes it much easier to tell when I'm stuck in the 5 second rule, besides.
Of course, as with all changes, this is Beta, so things can change, and Koraa is asking for focused feedback and bug reports on the concept, but it's something I'm certainly hoping makes it live.