DHA had a lot of potential, and while it does an admiral job nothing ever seems to be as quite as good as it could have been.
To start with, I found the main protagonist rather boring. This is probably by design as his very nature is to be the "pure innocent" who is tempted by demons, but I still think he's a little too generic and that the author could have done a little more. The same applies to the main heroine, as I find her fairly one dimensional as well. She has one defining feature in her love for the hero, but beyond that we really don't get to know her too much.
I did, however, like most of the 7 deadly sins, and wish more time could have been spent with them. As it is, we really only got little snippets of each (each one would have a chapter or two devoted to them), and it only served to whet my appetite as there looked to be a lot of interesting things there that could have been explored in a little more depth.
The story itself is fairly straightforward, with very few surprises along the way. I do feel that having the story compressed into two volumes meant a lot of the plot was sacrificed in the name of getting the full story in, and in this I really think if there were another two volumes or so it would have really given the story a chance to stretch its legs as it were. This really hits home when you get to the ending, which I thought was a rushed and confusing mess that really needed another chapter or two to tell properly.
The artwork is somewhat of a mixed bag. It's definitely seinen, but with a slight hint of that shoujo floweriness that gives it an interesting look. However, this is also a detriment when it comes to any sort of action sequence, as it just devolves into a confusing mess with little regard for how a scene should flow (again, I'm thinking particularly of the ending at this point).
All in all, DHA isn't a bad manga, it just had the potential to be a lot better than in ended up being. Another volume or two to tighten up the plot and also expand on the characters histories, and a bit more care when it came to the artwork would have done a world of good. Still, as long as you know what you're getting into you can still have a reasonably good time with this one, and it's short length means you won't be tied down for too long.
This one gets a recommendation, with reservations, from me.