Hmm, my initial knee-jerk reaction is mixed. I like the specializations that skills open up in the more complexity module, but the idea of taking multiple skill trainings in the same skill, basically bringing back skill points, bothers me.
I'm currently opposed to the modular approach to complexity Mearls has been proposing, because it doesn't allow for players that prefer differing levels of complexity to play the same game. As a DM I'd be either polling my players for what modules to use, and then we'd come to a decision for that campaign. But if you have Player A that only wants the core complexity, and Player C wants all the available modules, no matter which ones are selected, someone is going to be frustrated. In 4e, post-Essentials at least, I can accommodate Player A by suggesting they play a Slayer or Thief, where Player C can pick options from many sources for his hybrid Psion | Wizard.
I like that 4e is played mostly with the same rules from group to group. It makes it easier to find players, and I can go from running Encounters to playing LFR, to playing in a home game without relearning the system. I'm not opposed to house rules (and I join almost all players of 4e I think when I wish the CB supported them better), but I'm glad the base rules stay mostly unchanged from product to product.