The first thing to notice is the style. Think Tim Burton, anime-style. It's a unique style, strange enough to be interesting, just silly enough not to be depressing.
The basic plot is somewhat unique, too. Kids fighting monsters isn't new, but the setup of weapons/technicians isn't something you see every day. It leads to a good setup of emotional tension both between the kids and between the students and the teachers.
If you want to be jaded, you can just say, "oh it's just another shonen fightan series," just the same way every romance story is "lol it's just boy meets girl." You'll have seen probably every element in Soul Eater before, but the series manages to put them together in such a way that you get some good action, drama, and intrigue out of it all.