I've owned a G34 and the mag release is good, there are also other releases available to the Glock pistols from aftermarket companies. Not as good as the Smith & Wesson MP9, but with enough training which = familiarity, mag changes should be just as good.
With that said, one of the major differences is the interchangeable palm swell which allows the shooter to choose the most efficient grip and normally enhance the magazine release accessibility. Coupled with a highly ergonomic grip, it's really hard to fault the manual of arms on this pistol-or to fault the pistol at all. I'm a firm proponent of any pistol that allows the shooter to semi-custom the grip to right size via back-strap.
As far as a review, posted one here. Did a comparison between the MP and the HK P2000.