Well, the fact that it has both 3.x/Pathfinder fans and 4E fans interested and enthusiastic indicates that it must have
something going for it, it seems to me
From my perspective it combines some of the mechanical "tightness" and coolness of 4E with lighter combat (TOTM) and what is designed to be an "easy" introduction to collaborative world building.
The first part manifests in neat mechanisms like the escalation die (and how that interfaces with some character abilities to make combats about a rising crescendo rather than BANG-fizzle) and the non-grid-but-still-dynamic-combat that uses "nearby" and "far away" and "engaged" as its "zones".
The second part manifests in Icon relationships and backgrounds. The world background is meant to be an incomplete sketch - the choices the players make in chargen and in play drive the expansion of the background to fit what they are interested to explore. The "Icons", for example, are the "movers and shakers" in the world - and the PCs have relationships with them specified in chargen. There are 12-13 Icons (new settings would generally have their own set), but those the players pick as related to their PCs in some way will regularly be "pinged" to appear. Backgrounds are freely defined, and should ideally be completely unlike skills; "can handle a boat" would be a skill, "was once a pirate off the coast of Altania" would be a background. If, previous to chargen, there were no pirates off the coast of Altania? Well, there are (or were) now.
If heading in these directions is of interest to you, then 13th Age offers an easy path from D&D in this direction for both GM and players. If the general direction doesn't interest you there might be ideas you can "borrow" among the neat mechanisms included - but the
Archmage Engine SRD might give you those at no outlay...
Edit: d'oh - and I forgot the One Unique Thing, which both makes your character special/gives a reason you might be a hero and gives an opportunity for players to contribute to world building. It's part of my "second part" features.