If the anime gods granted me one wish, it would be that Inuyasha would go on forever!!!!
That aside, I would have to say that the most irritating and disappointing series ending was Neon Genesis Evangelion. I felt like screaming at the end!
I was glad to see they made a movie to end it properly after all us fans freaked out over it. That was somewhat satisfactory to me. I also didn't like how Cowboy Bebop ended, but I really wasn't surprised considering Japanese shows tend not to have such a happy ending like we Americans desire. I'd really like to see most animes continue past their ending!!!!