I've been extremely pleased with the sorcerer since its release in Players Handbook 2. I played a couple of sorcerers in 3rd Edition, mostly because it was a new class, but never really appreciated it since it was basically a wizard with far less flexibility. Sure, you didnt have to prepare spells, but your selection was pretty sparse and you couldnt use Metamagic feats effectively: stripped-down, spontaneous arcane spellcasters.
The new sorcerer fills in a different role from the wizard (striker), and commands raw magic within her blood. This was always implied in 3rd Edition, but didnt get touched on until later supplements. I'm happy to see that its gotten a better treatment, which saw two spell sources: dragon and chaos. Each relies on a different secondary ability (Strength and Dexterity respectively), but in case those arent enough Wizards has added a third in Arcane Power.
The cosmic spell source is tied to the sun, moon, and stars. Its tied to Strength, so dragonborn again get some love with the sorcerer. What differentiates it from the dragon spell source is that you choose a "phase" during a short/extended rest, each granting you a different benefits. The sun phase deals fire and radiant damage to adjacent enemies at the start of your turn and grants resist 5 cold, the moon phase boosts your AC by the number of adjacent enemies and grants resist 5 psychic, and the star phase lets you teleport when an enemy misses you and grants resist 5 radiant.
Here's the rub, however: when you first become bloodied in an encounter or use a daily power, your phase goes up to the next phase before starting over at star.
This works well with the concept of cosmic magic: your abilites are in a constant state of flux. This reminds me of the vestige pact, which had a similar degree of complexity since the benefits of your at-will was different depending on the vestige you had active. I think that the sorcerer at its core is a really fun class by itself, but the cosmic spell source will be attractive to more dedicated players since your abilities jump around.