Yes! I've played all of them except AAI2 - to my knowledge it's never been localized except for fan-made ones.
I got Ace Attorney Dual Destinies about a month ago, but only got as far as the second case's initial investigation. For some reason, it's just not as gripping as the previous games to me. Usually I can't put them down after I start, but I'm almost forcing myself to investigate in this one. Maybe it was because I was really looking forward to more familiar faces, and all these replacements are kind of disappointing. I love Gumshoe, and I see no reason at all to replace him.
I love Gumshoe as well, but I think that Fulbright is a great replacement and step-up over AJ Ema (She's one of few characters that never really grew on me, as much as I liked Apollo Justice. Loved her in AAI and Ace Attorney, though). I understand wanting Gumshoe back, but given that he's played a major role in five games (as well as the fact that he works for Edgeworth mostly, so there'd be little reason for him to come back), I think it's fine that they didn't bring him back for this one. I mean, they bring characters back all the time, so when they introduce new ones, I think it really hits home on the charm that made the original games so attractive to begin with.
And really, I think they did a fantastic job with Fulbright, especially as he develops and you get to see more of his relationship and chemistry with Blackquill. He's well written, funny, and I just think he's a good fit. Though I guess he gets better in the later cases, since I think the cases after the second are the strongest ones.
I do understand what you mean, though, as much as I loved DD, there was something about it that had me less gripped than the others. I can't really say for sure what it was, especially considering that they basically went all-out on this one, as far as mechanics, quality, cinematics, and streamlining were concerned. This was more the case in the Youkai Trail than it was with the others, but it kind of persisted throughout, and I'm not completely sure why.