I think the thing I've heard about DX3 that irritates me the most is how they say it will occasionally shift to third person to show your character "doing cool stuff" (their words), such as when taking cover (apparently it's a cover-based shooter) or when using certain biomods (like the conceptually ridiculous "multi-kill").
The first two games went to third person during dialogues and cut scenes, which is fine and seems to fit with the overall presentation, but switching to third person during gameplay based on context is something that really aggravates me in first-person games (see also: Turok). I find it jarring to be arbitrarily yanked out of my character's head and then crammed back into it.
If the defense here is that certain gameplay elements wouldn't work well in first person, then those elements should not have been part of the design in the first place. When making a first-person game, I feel that maintaining the first-person perspective (at least during gameplay; maintaining it at all times is a bonus) is vital to the feel of the game.
Interestingly enough, I don't generally feel this way about third-person games that have first-person modes for aiming, or crawling through tight spaces, or other situations where third person wouldn't work well. I guess I see first-person as an attempt to place you, personally, into the scenarios you're playing through, whereas third-person puts you more in the role of an observer; thus, while an observer's position doesn't really matter, having your viewpoint removed from your body is disorienting and breaks the flow of the game.