When Vanilla WoW first launched talents were based on trees, spec'ing down into a specialization would open up new options – but nothing stopped you from choosing talents across specializations and creating hybrid specs (though hybrid classes wasn't there – so it wasn't quite as flexible as dungeons and dragons charactes), of course this was highly discouraged since at endgame those low-level talents you'd be missing out on were crucial for being competitive. This remained the case until the end of the Wrath expansion – the only real change being that the trees got longer and longer and some of their content got altered (sometimes with big changes – I still miss being able to mana-tap my warlock from my pet even if I was apparently the only warlock who did NOT think that talent was worthless).
So talents were flexible in theory but not in practise – in practise it was cookie-cutter spec's all around, people looked up specs from theorycrafters and used what was rated 'best' without ever having any real opportunity to play around with it, at least, not if they wanted to avoid losing all the time.
Mists of Pandaria with it's new talent trees seems to have set out to really change that. Unbinding talents from spec was a great step, and now I understand why the trees are so much shorter. This allows for the talents to be much more powerful and game-changing while still giving you real choice at each level. The idea of course is (in theory) to balance each tier of talents so you can really choose any of the three available even at end-game and still be competitive. The only real issue will be if you choose with PVP or PVE in mind. Just how this plays with dual talent sets I'm not sure yet, perhaps you can only dual spec not dual-talent anymore ? Or can you have two each with it's own specialization and talents (that seems more sensible to me) ?
So that's what mists is trying to do in theory – make talents finally flexible, let players finally have individual choice. Of course no amount of balancing will ever be perfect, there will always be that 1 or 2 percent extra from a certain talent in most raids, and that's fine the hardcore raiders will use the cookie-cutter builds, but the rest of us who play this game for fun and not for a job, we will finally get to choose the talents we like best without feeling like we're letting our team down by not having chosen differently.
Of course it's not all perfect first time round. The druid community seems spectacularly unhappy with their current list of talents, while warlocks seem mostly quite ecstatic about theirs. The druid's major complaint though is that they don't have any true game-changers, just nice utility cooldowns. Of course that does work, and you get to choose the utility cooldowns you like best, but it's not that awesome "I can change how I play completely if I feel like it" feeling that some other classes got.
That may be a valid critique but if the worst thing you can say about the talents you can actually choose to choose from is that they aren't "awesome enough" that's a win in my book for such a radical structural change (although as I see it, it's a change which finally enables what WoW had first intended 8 years ago).
Even so, I looked over the current list of druid talents and I think that while they are indeed mostly cooldowns, they are actually really sweet cooldowns. Mighty Bash for example basically gives all druids in all forms access to a Tauren War Stomp for example, an extra stun for my kitty when I'm in trouble – hell I'll take it !
Disclaimer: I have read nothing I could avoid about the new MoP zones or their levelling or their content, I have not been on the PTR or in the beta. This is my OPINION on the posted releases and theory discussion around the talents but I haven't yet tried them myself as I want to avoid spoilers and discover Pandaria properly the first time I go there. How well this works in practise is yet to be seen – but I like the idea.