Flight model seems very similar to me. A lot of the LW planes seem to perform somewhat better than they did, but I am probably just running into less-skilled opponents.
On the plus side-
GVs. If you liked GVs before, you'll have a ****ing blast in them now. Forests full of rubber trees to hide under, tunnels, bridges, random little hills and valleys for cover. On the down-side Panzer IVs are still Hizooka-fodder, but I'm sure that'll be looked at sooner or later.
Graphics. Graphics are a lot better in my opinion. Sure, you won't see much of the neat little bullets holes (Hizookas still blow entire parts off planes, they don't just put a hole in things), but it is neat to see a hole in the cockpit glass or the wing. If you get a pilot would, blood sprays all over the cockpit, if you get your oil hit oil does. Rather interesting and fun.
Clouds and sun. Ever so much better, in my opinion. Some people complain about the way the sun is modelled... I don't get a headache from looking at it. But it is big enough to "hide" in now, which is cool.
Fuel Porking. It is gone. 75% is as far as a field can be dropped.
On the "down" side
Gameplay. Still stale. Nothing much has changed here. If anything, people have gotten even more timid than they were when you left. Typically, you won't find an enemy that will engage unless he has alt and numbers. TOD may change this, or the game may be to far gone, it is hard to say. And actually, I doubt if HTC even sees a problem with the gameplay, crowds in the MA are bigger than they have ever been, so unless they are all two-weekers, they are making more money than they were this time last year. So you'd probably miss actually fighting, but a lot of "vets" seem to have adjusted well and have taken on timid bore n zooming and ganging as their modis operandi.
Bottom line, in my opinion. If you left because of the stale gameplay, you'll be sick of the game in two weeks or less. But I'd say try it out for a month or so, you won't lose anything except 14.95.