Strangely, in the two dock scenes this ship looks much like the 1701-D minus the swan-neck pylon. Covers a lot of generational/evolutionary 'bullet-points'. Really impressive re-working of the design.
The Avenger design with the lengthened nacelle-pylons also is an improvement over the original; think of the scene were the Enterprise blasts the Reliant nacelle - when it's sheered away, just a little more movement upwards would have seen the lower hull breeched badly by the nacelle's tail end. Under other circumstances, it's a StarFleet crew who would've suffered for that design-flaw.