There are quite a lot (and at least one very heavy) discussions about sorcerers vs. wizard and the casting progression - balancing the sorcerer against the wizard.
I don't think the casting progression needs much work. The sorcerer might be slightly inferior or superior in this specific area, but I don't really think the differences are great.
However what bugs me is, that the sorcerer compared to the wizard is such a "idiot savant". He can cast spells. Great. No need to prepare. He's not devoted to this stuff. Defining for the sorcerer, compared to the wizard, apart from being able to cast somewhat more spells, though, are the bloodlines. This is what gives him his powers. It should have a high impact for him.
The bloodlines are very neat, but as I percieve them ingame so far, not defining enough. The low level powers mostly become irrelevant quickly (dealing 1d6+1/2 sorcerer caster level damage? Nice at level 1. But at level 10? Or being able to do 2 melee attacks with claws? With low attack progression? Would only make some more sense if you cross class into some high-attack-power class, but then you don't benefit from the higher bloodline effects.)
So I am not yet convinced the bloodlines (which are a great idea) play the role they should play. They should IMO be a lot more relevant to a sorcerer. At the moment the bloodline is an addon to the sorcerer, but the way they are described it feels to me a bit more like the Sorcerer should be built around his bloodline.
To further this, bloodlines could have effects on how a sorcerer chooses his spells or action in combat or out of combat. The sorcerer should be more compelled to use his bloodline powers. At the moment some of the defining "active" features are hard to use at later levels, because their effectiveness does not increase (see above) and because they have little impact on the overall behaviour and tactics of a sorcerer. Some seem bad choices even (Abyssal Bloodline claws? See below.)
For exmaple: An elemental bloodline might deal additional damage with spells of some specific energy (like fire) or raise the save DC for such spells or the caster level.
The claws for the abyssal bloodline are nice, but it would be better and more defining if such a sorcerer would be actually compelled to use this class feature: Give the claws additional attack bonus with time (maybe so that using comes a bit closer to medium attack progression) along with something that protects the sorcerer a bit, when forced to fight like that (who goes into a melee, even with 2 claw attacks, with low hit points AND armor class?).
I don't have it all worked through yet, but I think the examples above explain what I mean?
Another thing that bugs me is, that a sorcerer is such an "idiot savant" compared to the wizard. The wizard gets 2+Int skill points, just like the sorcerer, but oh look: The wizard uses Int for casting, too. So he has more skill points.
The greater choices in skill selection AND spells (along with the "un-staggered" progress in gaining spells) are not yet compensated by the sorcerers bloodlines and more spells.