In terms of mechanics and gameplay, DA:O is -- in my opinion, of course -- by far the best of the three games. I much prefer it. I prefer DA:I above DA II in every way, and overall I'm actually rather fond of it, but map in DA:O's gameplay instead and I'd be much happier.
However, as much as I dislike the trend we've been seeing lately in the mechanics of BioWare's games, I can't say that it's necessarily a new thing. The moment they stopped using licensed combat systems, it's been all over the board. BG, BG II, NWN, and KotOR were all adapted from licensed pen and paper systems (all basically D&D/D20 system for KotOR), and DA:O has been the one exception to a game that I liked mechanically from BioWare since then. So I'm not sure that it's actually due to any particular shift, rather than their continued experimentation. I would certainly have preferred that they settle on one general mechanical design per series, at least, but at this point I'm no longer surprised when they shift all over from game to game.
Some people prefer one combat system, others prefer something else. It is unfair to condemn one game because of personal preference. Some like to have auto dodge, auto attack while others like to be more hands on. The luckiest are the players who can easily adapts to different systems. 
I think that, between DA:O and DA:I, this is really what it boils down to. There are many things about DA II's combat that I would consider to simply be poor combat design; DA:I is mostly decently designed mechanically, but not at all to my taste (I do like the game despite that, however). DA:O is also well designed, although not perfect, but far more to my taste mechanically.
I can and do easily adapt to different systems in games, but I have a strong preference for auto attack and auto dodging
in RPGs because I feel that's a better fit for the genre. It represents more fully that it's your character who's doing the attacking, and you're controlling your character by coming up with the strategy and building the character as they level up and so forth. I'm actually fairly fond of action combat, in action games -- I like first-person shooters, for instance -- I just don't feel that it mixes well with RPGs. It also often creates a disconnect between the lore of the game world and what one hears in character and the mechanics, and that is not a good thing. It's a problem I have with DA:I.