Well, both Soul Eater and Ao No Exorcist's anime endings episodes are bad since they aren't canon.
Ao No Exorcist anime follows the manga plotline completely; up to the point Rin faces off with Amaimon for the second time. After that, it's a lot of bullshit. I won't write all the points I disliked in it cause that might spoil many people but yeah, those "fillers" doesn't strike as much as the manga plot.
Still, if we consider that those were "fillers", then Ao No Exorcist and Soul Eater can boast to have among the best Anime fillers, duh ~`
I agree about the temporary wait but oh well, try explaining that to the greedy money-making makers of nowadays. U_U
For Ao No Exorcist, it's not completely off-plot. As I said, it goes non-canon post the 2nd time Rin and Amaimon squares off. Which occurs at the 17th episode if my memory serves me right. It "ends" at the 25th episode. Obviously, the manga story still continues. In short, Ao No Exorcist's anime has 15 "Canon" Episodes, 8 "Non-Canon Episodes" & 2 "Fillers". By fillers, I mean, real fillers; not anime-take episode. Like there's one where 3 of them go seaside & there's one when there's cooking contest
As for, it starts "slow". Well, that's basically the rhythm of the manga; though it's battle chapters are quite intense. Ao No Exorcist is not really the typical Shounen manga (like FT, Naruto, Bleach ect...) where in 4 chapters, you get random fights + some epic dialogues + some epic scenes + some fanservice + some humor. Sure, there's those elements in Ao No Exorcist but it also got a deep dark supernatural tone that gives a strong accounting on the "work" of Exorcism.
Also, it tries to develop its character' persona pretty slowly. In Naruto, for example, you get the small boy, learn of his past/present, get a gist of his attitude and learn of his objectives. In Ao No Exorcist, again, there's those elements but again, there's more to it. There are many secrets that got unveiled to Rin as chapters go on and we get to see lots of new persona developing into Rin. In a way, it shows its growth as a character; both power-wise and attitude-wise. However, in Naruto, FT, OP, Bleach ect... the main-characters grow in power more quickly and develop a new ideal post 20-25 chapters. Rin, on the other hand, grows stronger very slowly. However, his characterization keeps evolving after every 3-4 chapters. Add to that, most of the other characters also get a pretty deep presentation.
IMO, these 2 different takings on the tone and characterization induce a slow-moving chapters. And it slackens a bit more since there's much less humor in Ao No Exorcist; compared to usual Shounen mangas. Still, I personally like it; as it fits the story well. In a way, that's a bit my way of writing FFs (lots of build-ups and lots of character evolvment and fewer battle/powerups portions
), so maybe that's why I love it that way. Personally, I barely have complains on Ao No Exorcist; though I wished it didn't over-dramatize all characters and was weekly manga; instead of monthly.
I know that they're weekly anime and monthly manga, but I wouldn't mind to wait...if they had shelved it.