1) It is remarkably different from each and every other edition of D&D, this gave many veteran players pause. 2) It has very in-depth combat rules but handles any other situations (ie: skill challanges) in a very rules-light way. The vast majority of powers only have in-combat uses with only an handful of utility powers being useful outside. Rituals sorta patch that hole, but only for classes that have access to them. 3) While the economy works from a player balance prospective, the amount of wealth a paragon or epic level adventurer is carrying around is mind-boggling. In 3.X an high-level adventurer's gear is worth as much as a castle, in 4e it's worth as much as a nation. 4) 4e combat rules work pretty well and achieve a great degree of balance. That is at the cost of class homogenisation and of some degree of suspension of disbelief (it works that way because the rules say so, even if it's unrealistic). That said, while I started out as a 4e hater, this edition sorta grew on me, and I find it particularly good for combat-centred campaigns on virtual tabletops.
