Currently the finest flight / action sim on the market, at least until Ace Combat Zero comes out.
It's blazingly fast, accurate to a fault with improved physics, flight controls, minor squad based tactics, and better graphics over all it's predecessor's. AC5 is an absolute joy to play. The strategy aspects give it a real sense of tension and time constraint.
The evolutionary aspect of the aircraft is surprisingly innovative for namco, and offers vast replayability to retrieve all planes and paint schemes (it took me three and a half months to get it all).
The missions are normal fare, but all well-designed (though you'll come across a few rehash levels that are dangerously similar to AC4). Also the weapon limits are considerably tougher than the 99 missile capacity you could carry on all planes in AC4.
It's arguable that AC5 may well be the best in the series so far.