Having a significant place in anime history is not the same as being good anime. This is not good anime. The plot is terrible and the characterization is weak. The art might be the strongest part, but even that could be greatly improved. Many people have pointed out that this was the first anime directed by the director of Neon Genesis Evangelion, which makes this at least a curiosity, but does not make it a great anime in itself.
Why would pilots of spacecraft wear such skimpy outfits? How does the squealing and yelling of the pilots of the ships influence their performance? Why do the aliens look like bits and pieces of earth-evolved arthropods stuck together in random assorted patterns? How did Noriko develop an apparently serious relationship with Smith when she appears to have known him for about 5 minutes before he dies? What kind of a name is "Gunbuster?" Why do spaceships blow smoke when they accelerate in the vacuum of space? Why do teen girls subject to emotional outbursts at the least insult or disappointment get chosen to pilot the spacecraft upon which the survival of the human race depends? Why is music lifted from Handel's Messiah for the final episode, and why is that episode largely in black and white?
This series should be appreciated for what it is. It should be given credit for its place in anime history; it was made in the 1980s and should be judged with the standards of its time in mind, as much as we can do that. But even though anime has changed greatly since then, writers did know how to write good plots, good dialog, and believable characters in the 80s.