Star Wars Clone Wars was great, but it wasn't the last good Star Wars series. Star Wars: The Clone Wars (2008-2014) was a great series and, in my opinion, better than the older animated series.
I know I'm not going to be able to enjoy Star Wars: Rebels the way I liked The Clone Wars, I'll still watch it, but The Clone Wars was a recent and great animated series. So to answer your first question, great cartoons still exist, but are few and far in between.
As for Halo getting an animated series, I wouldn't be against it unless it meant we couldn't get a live-action series. (Which is something I've really come to prefer for a war type of genre)
Halo: Nightfall will be releasing in the future and I'm very excited for it. I'm sure we won't be disappointed.