I fear this great episode is so great because the producers saw the writing on the wall given how Syfy is treating other scripted series at the present time. The ending is hopeful, bright, and looks towards the future! It wasn't a cliff hanger and actually provided endings to the outstanding questions without creating major new ones. It really was as more of a proper series ending than it was a season ending.
The other reason, I fear I'm reviewing a series and not season ending, is the cost for the new sets, as well as the actors for a fifth season. Syfy seems to be cutting costs and not setting itself for high costs. I suspect producers decided on a proper ending that left Syfy with a choice -- renew with a proper commitment or keep this proper ending in place. I see this as a VERY RESPECTFUL to the fans ending. (If only other series of our past had had the same opportunity / chance.)
Should this analysis be right, I applaud the producers for putting the fans, the characters, the story line first and giving us a great ending. IF on the other hand it is a season ending, WOW!! Simply great, wonderful, and outstanding of a way to end one arc and obviously set yourself up for another one!! I can't wait for season 5 (and hopefully 6, 7, and maybe more). I love series that do arcs and obviously it can be successful - Stargate SG1 did arcs both with the same characters and with new ones.
Yeah, I see hope for a new arc and multiple seasons , but I also see a basis for fear we saw a series and not season ending. I'm going to go with the positive - the glass is full until Syfy says otherwise! So, WONDERFUL, GREAT, OUTSTANDING, SUPERIOR season ending!! (or thanks for honoring us and everyone else.)