The is the fundamental problem with talent points as used in D2 is that they completely destroy flexibility. Because skills get more and more powerful per point for each point invested in the skill the only reasonable approach to character building is to slam the maximum legal number of points (20) into each skill you intend to use. This also means that if a max talent skill is balanced against monsters at a particular level then any skill with only a few points is utterly useless at the same level, which means that characters end up putting all their points in a single skill and never doing anything else throughout the entire game. This was compounded further by making skills multiply together so that after you put 20 points into Nova you have to put 20 points into Lightning Mastery to make Nova better. This means that until you are extremely high level there is no chance of ever using any spell except Nova - hardly a recipe for deep play. This lead to messes where low level characters never wanted to invest more than 1 point in anything because they didn't want to waste points in a suboptimal skill and saved up all their points until they could get their best skills at level 30. Having the best strategy being 'don't spend any points and get boosted to high level' is a craptastic design by any measure so Blizzard solved it by bringing in synergies that only made the problem worse by making it optimal to use 100+ skill points on a single attack skill!
This is all a disaster. The problem is that when you give players a resource they can spend usefully to make a single attack better they will spend all of those resources on that attack and if each point of the resource has some real marginal benefit then that attack will eclipse all other options. Even if your attack is an AOE you end up using it for single target when it does enough damage, and that leads to repetitive gameplay. It is important to give players options to improve or modify their abilities so they can have control over how they specialize but that control needs to be limited. The current D3 system looks wonderful in that players learn new abilities as they level up and the abilities scale with level so new abilities aren't necessarily better - just different. You then get to 'equip' 6 abilities at a time of the 20 or so that you have so you have a truly stupendous number of different setups. Each ability can also be modified by runes to behave differently in 5 distinct ways so even if you have the same 6 abilities selected their performance and usage will vary person to person. I really like this setup because you get lots of control over what sort of abilities you have and how they work but you retain lots of flexibility so you can approach different fights and situations with very different tactics. Assuming Blizzard gets the balance at all right you will be using different abilities depending on what sort of situation you are in and who you are playing with.
We lost skill points but we gained what looks to be a much better system. The only potential drawback is that you have unlimited ability to respec - any time you are out of combat you can swap around which abilities you have 'equipped'. This means that any level 50 Wizard has the same potential as any other and there is little reason to replay a class because there isn't a Frozen Orb build or a Nova build but rather just a Wizard who can equip whichever abilities they like at any given time. I think though that the lower replayability of the levelling game will be more than made up for by the levelling game being better and endgame characters not being caught with a skill point or two spent poorly that can never be undone.