I thought Carnivāle
had a very satisfying ending despite it's open-ended conclusion, which was a natural result of the first two season intended be the first of three chapters. Sure, we don't get answers like "Did Jonesy survive?" or "How will Brother Justin and Ben recover and face-off again?" but what otherwise, the show had a clear beginning, middle, and end in the first two seasons, which is probably why HBO was fine with cancelling it. Daniel Knauf has since mentioned in interviews (including one this year at A.V. Club) about the different character fates and how the show would have progressed in general.
Likewise, I think Deadwood
had a natural conclusion after three seasons despite leaving things hanging with George Hearst. Besides, we wouldn't have been able to see Hearst get his proper comeuppance consider he lived for many more years and served as a U.S. senator.
Lastly, I think Rome
had a solid conclusion after just two seasons, although the show did get some forewarning, hence the fast-tracked timeline in the second half of the season.