One really good thing about this system is that it allows for relatively easy insertion of more complex material. If designed correctly the baseline fighter-killer subclass can compete handily with a more complex fighter-duelist subclass just by hitting harder. For advanced players this will be indistinguishable from simply adding new classes on but I suspect choosing twice from two lists of size four is much more palatable to newbies than once from one list of size sixteen. In third edition the only way for a fighter to distinguish himself from another fighter was taking different feats and those usually relied on a lot of system mastery to evaluate and plan out. The new system should hopefully reduce the need for system mastery to be competitive. It is much more restrictive than third edition too but I feel like this will greatly enhance the experience. While individual players have fun making invincible characters it is much more fun for the GM when player power is more predictable and new players feel better when their characters matter.
This system makes me more optimistic than I was before about how much fun playing the Basic system will be. With only four classes and no other significant choices I really felt like the Basic system as presented awhile ago was utterly boring. I do think there is something to be said for keeping the number of choices and the difficulty of those choices down for new players though and this new subclass system looks like it hits the sweet spot. Hopefully they can find a way to apply it to skills also as that would really get me behind the system as actually being good at the whole complexity scaling thing.