Some stuff probably needs to be addressed (the cavalier hybrid probably needs some sort of hybrid "update". If only making it's OA power an Immediate Action, to prevent it being a full defender in terms of 'mark+punishment' regardless of the other half of the class.
Similarly, the monk's unarmored defense and avenger's armor of faith require hybrid talent, but the vampire gets it's reflex right away (it is a shield bonus, while the others are untyped, so that could be part of it). Consistency would say it probably has to be put into the hyrbid talent options, although it would probably be better if the other features were put into the original class (or perhaps put into 'equivalent of leather/hide armor in determining worse of 2' ... with the unarmored agility being the equivalent of adding a heavy shield). They would probably need to make sure the class features don't stack if they did that. [Altough, at the moment, a vampire + monk or avenger with hybrid talent can have some awesome AC the way things are. A monk/Avenger [or swordmage] can do that now, but it does require double hybrid talent, and thus needing to take the hybrid paragon path.
The "able to use MBAs for striker bonus damage" for the executioner assassin is interesting, and could become more so in the case of classes with a "counts as MBA" power. An executioner/warlock, for example, could use eldrtich strike (or the new feat) to use a warlock mba and get both curse damage and executioner bonus damage on the same attack (and throw assassin's strike on top of that). They may need to clarify things to avoid those kinds of loopholes (i.e. only MBAs that don't have a class/level associated?)
Another unintended consequences thing to test would be archery mastery. How would in interact with say, a ranger/warlock hybrid. Would it allow for use of both quarry and curse? It would be interesting to see a half-elf picking this up by grabbing a ranger power via dilletante, and then having fun with it with "counts as rba" powers. A half-elf mage would have some fun with magic missle combined with being able to slide/prone/slow(s/e) or make it a burst.
The vampire stuff at least creates some interesting options via hybrid or multiclassing into vampire. Considering stuff like the backgrounds which determine hp based on different stats ... someone can dump stat con and multi into vampire and have some interesting stuff going on. A martial or primal defender could make use of the extra surges and extra regen. Psionic/arcane controllers on the other hand can, if they are succesfully protected by their allies, benefit greatly from alternate outlets for 'extra' surges ... especially as they would have lots of extra surges in a fight. The Psionic Vampire is especially interesting because, if you go with minimum augmentation, you can get a lot more healing surges (potentially). The thing to remember with those is that, unlike blood drinker, you don't get to keep trying to hit, so you could miss with an encounter power and lose a chance to gain a surge (also, encounter powers without attack rolls would be wasted ... so multiclassing from knight or slayer into vampire may not be the best idea.