Fair enough for the first part. And I agree, character development-wise there's not much I can remember. Though you did get some more insight into why some characters act the way they do, Draco being an example.
The first 2 books aren't the longest (and being the first two written...) so I wouldn't take those 2 as an example of how the entire series continues. Not saying it does a 180, but it gets better. At least somewhat. Not sure if it'd be enough reason for me to tell you to read them. Probably not. Just know that the movies (at least up to the 5th, haven't bothered watching 6 and 7) don't really do them justice, imo.
It feels more like it's just losely based on the story so far, not necessarily meant as an actual continuation. Draco's personality felt far from what he seems to be there (not like we saw much of anyone else, I guess Tonks feeling *very* off as well on the first impression). He's... a lot more "wimpy" from what I remember. Doubt he'd have the balls to go through with what he did so far. Then again, it seems *some* time has passed at least, soo...
