Yep, it's sad but the RvB series has come to a close. Perhaps it's for the best, having a definitive end to it. Better than people just losing interest and having it die off slowly.
It's a geat episode to, not the fuuniest one they've ever done, but a good one. It's over 10 mintes long, and there are 3 versions with a different ending in each one.
Though the series may not be done with quite yet. The way the episode ended (in general among the 3) seems like theres still more to come. People who bought the Limited Edition or Legendary copy of Halo 3 may get one last episode from them with the bonus disc.
The DVD for the 5th season should be out at about the same time as the current schedule for Halo 3 as well. But for now let's just enjoy the last episode.