Glen A. Larson has been known to take succesful movies and "creating" a new TV series from its core concept. (Battlestar Galactica/Star Wars, BJ and the Bear/Smokey and the Bandit, Automan/Tron.)
This was his first, taking the success of "Butch Cassidy and the Sundance Kid" and cleaning it up for last 60's prime time, what with the "nortiuous outlaws but never killed anyone, so they're really OK guys" bit.
However, the result is really quite good. The two leads have good chemistry and banter, the plots are very well contructed, and the guest stars are a lot of fun.
I suggest watching Butch & Sundance before watching the series again, it's very interesting to see what was lifed and what was not (there's even a line in B&S "Which am I, Smith or Jones?" when they attepmt to go straight.)
I'm watching the whole series on the Western Channel now, and enjoying it (note, the Pilot and the Day They Hung Kid Curry are 90 mins, and not part of their syndicated package. Hunt the Internet for those until a DVD is released one day.