I felt exactly the same way. :(
We already know why it ended so bad but yeah; the author had to rush the ending since he got axed. As he finished the manga, Ken Akamatsu (the mangaka) hinted that he might release a new project related to negima. A lot of people doubted it ever happening, but as a Negima! fan, I'm happy to say that he didn't disappoint as he recently released his new manga: UQ Holder!
It's the SEQUEL to Negima!, so if you were disappointed with the ending (which I'm sure everyone that read the manga was), I REALLY recommend checking out UQ Holder!
Just look for it in your favorite manga site (I go to mangahere) and give it a try. :D