First and foremost, I didn't enjoy DA2 as much as DA:O for many, many reasons. Indeed, I've not even bothered playing it a second time, compared to DA:O which I've played through multiple times. DA2 simply hasn't appealed to me enough to have any desire to play through it again.
In terms of this discussion though and having given it some thought, as far as my own thoughts go, there's one aspect that can probably account for at least one key difference between my enjoyment of ME2 compared to DA2.
That key difference is continuity. Now the continuity aspect for me, was on two levels.
First and perhaps foremost, between ME1 and ME2, there was continuity of story and characters. Even if original squad characters weren't part of your squad in ME2, then they were factored into the plot meaningfully enough if their role was quite small, or there was an opportunity to interact with them in more detail, or engage in a quest where they featured heavily.
In essence, I felt as if I was continuing the next stage of the lead character's journey (which I was controlling), accompanied by, or involving at some level, characters I'd come to know in the previous game.
Insofar as the other aspect of continuity, although ME2 evolved significantly as a game from ME1, the way the game played to me, it felt like a natural evolution. Even though there were certain elements of the gameplay that had changed, what essentially drove the game and my interest, was the story unfolding before me.
So, moving from DA:O to DA2, having pre-ordered the game based upon my enjoyment of the former, although I was expecting some evolution between the two games, I was hoping for some continuity of the story that had begun with DA:O. Clearly upon starting my, as yet (and likely only) play through of DA2, it soon became obvious that the story unfolding wasn't going to offer a continuation of anything meaningful from the previous game. Now although I could accept that to a certain degree, I think what elevated my dismay in the story for DA2 was the cameo appearances of characters from DA:O, in such a way that I felt they were'nt really needed, but just thrown in for the sake of it.
Insofar as story continuity between the two games, it's probably fair to say that the new story didn't appeal as much to me, as much as a meaningful story that featured the Grey Wardens or other factions and characters from DA:O may have done.
Finally, the evolution or changes in gameplay on so many different levels, removed any feeling of continuity that I was really playing a Dragon Age game at all. Indeed, Dragon Age 2 has some redeeming aspects to it, but even though it was marketed as "the sequel" to Dragon Age: Origins, I just didn't feel the same level of continuity that I enjoyed between ME1 and ME2.
Hopefully that might explain one person's thoughts on the subject at hand. I'm not interested in the bickering and the OP raised quite a good question, that will result in many different answers, depending on different people's perspectives for all four games.