About Me: I've been playing DnD since 1980 (tons of AD&D, Basic, Expert, Companion, Master, 3.5 and 4e; a little 2e). I've been DMing since a few years after starting playing.
My first impressions of the new edition are intensely negative. My main concerns are:
--This is a return to 3.5, with a few elements of 2e and 4e thrown in, and some original twists on old mechanics. I loved 3.5 back in the day, and played it a lot. But I've moved on, and the things that I really liked about 4e (more on that below) have been jettisoned, whereas many things I intensely disliked about 3.5 have been brought back.
--A return to basic attacks for martial classes and monsters. This is a killer for me. I don't think I will be able to take the monotony of playing a martial class whose turns consist of 'I move and attack' repeated ad nauseum. One can say, 'Well, improvise!', but not everyone wants to do this or should be required to do this. My wife plays with us and is a newbie; she won't like having to try to work with me to invent rules on the fly. Also, improvised rules are by their very nature potentially very different according to the DM; get a bad one, and the game can be extremely bad (this is a universal problem in any edition, of course, but it gets far worse when the solution to a lack of mechanics is 'Improvise!').
--A return to rolling for HPs. I know we might get the option to just take a standardized roll, and I will definitely be using that if it is in the game... rolling for HPs was just a recipe for frustration when my group played 3.5. I thought that 4e had advanced beyond that.
There are some things I very much like about the materials. The new HPs are fine. I like the return of damage types (slashing, etc.) for weapons. I even like the return of some of the old-school spells in a way. But overall my first impressions are intensely negative. Seeing monsters and martial classes return to the 'move and attack' turn, with basic attacks being the mainstay of the class, is IMHO not a step forward, but a huge step back.
I'll post more in a couple of weeks once I run my group through the adventure. Hopefully, my opinions will change... but for now, I am extremely disappointed.
Hopefully, your mileage will vary.
"What is the sort of thing that I do care about is a failure to seriously evaluate what does and doesn't work in favor of a sort of cargo cult posturing. And yes, it's painful to read design notes columns that are all just "So D&D 3.5 sort of had these problems. We know people have some issues with them. What a puzzler! But we think we have a solution in the form of X", where X is sort of a half-baked version of an idea that 4e executed perfectly well and which worked fine." - Lesp