Let me first just say, "Woah." Perhaps even "Ho-lee carp!" Pretty much everything we've seen so far in the beta is nothing compared to this change, which will essentially halve the amount of talent points you'll be spending. Whereas a level 80 character right now has 71 points to spend, under the new system, you'll have 41 points at level 85. Furthermore, at level 10, you'll be asked to pick a talent specialization and you will not be able to spend talent points out of that specialization until you've spent 31 points in that tree.
Considering you'll only have 41 points to spend in total, this means that there will be very little talent overlap between, say, an arms and a fury warrior and as such, much less risk of an arms warrior trying to cherry-pick fury for DPS talents. Likewise, tanking warriors won't be going up arms to pick up Impale (unless it is very, very low in the arms tree), and you'll have to be level 72 before you even get to spend points outside your main tree (tour 32nd talent point).
To say this is "monstrously huge" is to dabble in understatement. The very method by which we choose talents is changing -- how we can choose them, and how often we get them. Many abilities that are currently class- or spec-defining talent choices will be linked to the talent tree you choose to specialize in, and passive abilities that currently exist as talents will simply be applied by making the choice between talent trees for your specialization.
There have also been heavy changes to how mastery works and what benefits you get from specializing in a talent tree. With the new system, you won't be seeing any bizarre talent specializations since there simply won't be any room for them; you'll level locked into one tree and won't see another until fairly late in the leveling process.
Does this mean that fury will be able to dual wield at level 10 rather than waiting for level 20? How many passive versus active abilities will the talent specialization grant? With talents like Anger Management gone and very few offspec talents left, one has to wonder about offspec tanking viability. Will crit immunity be built into specializing in the protection tree? Shield Slam as an ability gained via specializing takes away an ability that current off-spec tanks can use for tanking. Do we still even want them to tank, or is the design goal now that there will be protection-specced warriors (and paladins, and blood DKs, and feral druids) doing all the tanking from now on?
We don't know enough yet to really say with any certainty, but with Mortal Strike, Bloodthirst and Shield Slam listed as the active abilities core to each talent spec, it definitely seems like DPS-specced warriors will be losing enough tanking viability to make them performing in that role less viable. While they can certainly still strap on a shield (so far as we know, anyway -- for all I know, the ability to use a shield will be a specialization bonus), they're lacking Anger Management's threat increase to their bread-and-butter attacks and Shield Slam's big burst of threat.
So we have a pretty significant change to the mastery statistic as well. To a certain degree, it's just a nomenclature change ... having those passive abilities as part of talent specialization instead of mastery. But we now still have the mastery stat and a trainable mastery skill with stackable mastery rating on gear. Mastery seems slated to work in combination with your talent specialization rather than simply with the tree you spent the most points in (since you'll be declaring a specialization rather than just speccing down a tree), but at this time, it does not appear that it will work mechanically differently. Vengeance is moving to a passive protection bonus, apparently.
At this date, we don't have a lot more specific information to work with, but what we have is pretty astonishing. Talents will be far more important, point for point, in the new system because you'll have half as many points to work with. Your chosen tree isn't just meaningful or significant; it's of paramount importance, because you won't really be leveling with talents from any other tree. (To some degree respec and dual specialization will help out here ... One can only hope the price on both will come down.) Class-, role- or spec-defining abilities that are based on talents may become passive or active benefits of a talent tree specialization or may just be utterly gone. A lot of work remains before we know what we're getting, but this is major, and we'll pay close attention to it moving forward.