The first season of Babylon 5 is pretty terrible (TKO is the worst episode, almost worth watching just to see how bad it is). However it pulls a complete 180 and seasons 2-4 are some of the best Space Opera out there. Season 5 is mostly garbage. Don't let the low budget and terrible dated CGI turn you away, it's a fantastic show, a must watch if you are into the genre.
Star Trek: Deep Space 9 has a wonderful pilot episode but many solo/self contained episodes in seasons 1-2 are pretty terrible (Move Along Home is excruciatingly bad). Season 3 is when it finally gets excellent (Right around the time Sisko shaves his head and grows a beard). From there it gets better and better until the final season where they introduce two new characters who completely ruin the show whenever they are on screen (Vic and Ezri). The last stretch of episodes are great minus a disappointing final showdown between Sisko and another character.