It wasn't supposed to be an ending. The manga continues and thus the anime is going to continue. I'm just glad they are continuing this and hopefully the author can wrap things up and we get a finale season 4 sometime in the near future.
Just be glad they weren't Madhouse and decide to do an anime of Berserk and NEVER come back. Or do Claymore and decide to fuck things up in the end because they wanted a "real ending" vs. Ultimate Cliffhanger. Though both are equally shitty.