I felt the same way. Both are on different spectrums and the only thing truely tying them together is the ending for both.
Diebuster is so vastly unique and different from Gunbuster that hell, you can all it an alternate story if it wasnt for the end. I like them both for almost completely different reasons.
I cast my opinion: First few episodes of Gunbuster did seem a little boring to me as well as silly, in a good way. 5th and last episode were great but i wish it would of came sooner.
Diebuster made up for Gunbuster's early boredom for me with a fight every episode, only getting better and better (especially episode 4 and 5).
Inazuma Double Kick.
In the end, i ever liked or didnt mind all the characters. Lark kicks ass.