I usually don't really like the "magical being descends upon a loser" stories (aside from To-Love-Ru, because that was well done), because it just seems so... easy. A guy is bound to a girl that happens to be perfect for him because of some cosmic fate just seems too convenient of a story. I like romances that have to be developed.
And this is different, because the magical being is there to help, and is completely not a love interest at all. She is cute in a chibi way, but not in a way that would be acceptable to see her as a love interest.
The different kinds of magic are interesting, and they lead to some great scenarios. The author does a good job using the "10" gimmick to come up with a lot of plot lines. The main important part though, is that the author doesn't use this gimmick as a crutch, but uses it to further develop the story. (Spoilers) When the author reintroduced the tried and true idea of a memory wipe, and the misunderstandings that resulted after the earthquake, that's when I knew that this mangaka knows what they're doing. That's the proper way to progress a story: to hint at her feelings, but draw back enough so that the story can stay back and not be too rushed. To me, it's a perfect way of pacing. We understand her character, but then all of that is quickly negated. It is not done in a frustrating way, because her feelings are still there, but the only progress of bringing out that feeling is stunted. And that's much better than eliminating her feelings altogether. (Spoiler end)
The art is great. There's a lot of humor. Very little fan service, but that's ok for me.
The bottom line is, it's just well executed. As with a typical harem, there are more love interests that are introduced, but the great part with this story is that more antagonistic characters are simultaneously introduced as well, leading to a very real possibility of a conflict directly related to that new love interest.
The concept may be cliche to you, but the plot and the characters allow it to remain very fresh and entertaining.