This is the most important part of cata they have to get right or it will die immediately. Cata is beloved by the PvP community as one of the most balanced instances of the game, ever. This is mostly due to the way they handled talents and the way they gave more classes interrupts etc.
The PvE from what I hear is really good as well.(outside of DS) I only have first hand experience with BWD and TB while they were current, but I’m sure messing with talents too much would screw the later phases as well.