Personally I love these new formal uniforms, especially in combination with the on-ship uniforms. They have the same formality as the old movie maroons but in a simpler and more somber style, which seems very Starfleet and appropriate for the more restrained fleet of the AU. It feels a lot like an actual Class A uniform but stripped of a lot of the militaristic flash. Meanwhile they still have the more comfortable and practical-looking uniforms for on the ship instead of having everyone prancing about in full multi-layered dress all the time.
The field jackets are pretty sweet too. I like that they replace the bright colors that are great on ship but a bit too "shoot me now" with a darker grey, while still leaving those little windows for the colors to show through. Again, it's something that seems very practical, especially compared to the big bulky jackets from TWoK that were put over the already-thick uniform. Also, I whole heartedly approve of the wet suits. Kirk and McCoy should spend the entire next movie in them.