Martian Successor Nadesico is a rarer kind of comedic
anime. Most of the hilarity revolves around the very silly quirks of the various crew members and the improbable circumstances that they get themselves into. It's somewhat similar to
Irresponsible Captain Tylor.
Yet, there are some elements of the series that are definately not funny. As the characters begin to mature and grow attatched to one another, the angst level rises significantly. The series turns bittersweet. One source of the sudden seriousness is the relationships that develop between the characters. Another is the growing ambiguity about the true motivations and morality of the various powerful forces in the Nadesico world (Nergal, the UFF, the Jovians, etc).
For example (some spoilers ahead, read at your own risk), take the relationship between Akito Tenkawa and Yurika Misumaru. At the start of the show, it's a rather sterotypical comedic anime relationship. Yurika is madly in love with Akito, and Akito is really not that interested in Yurika. She is entirely oblivious to all of his hints. By the middle of the series, however, the relationship grows more unstable. When Yurika is forced to kill the Martian survivors, she desperately needs emotional support. Instead of recognizing that, Akito turns her away like everything is normal. The rejection deeply hurts her.
Martian Successor Nadesico makes the shift between comedy and tragedy smoothly and oftenly. I really enjoy that aspect of the series. Still, it is predominantly a comedy.