The writers never had any intention to give it a "real ending." Their plan was to develop the characters for as long as the network would renew the show. There were not going to any specific place with the story. This is what Ira Steven Behr has been saying for at least a couple of years, and it shows.
It sucks that it's over, though. It was a fun ride. The best shows get cancelled before their time, with very few and very rare exceptions.