I'm going to mostly mirror what other people have said. Below I have listed items that I deem critically important if not for this release, then some point in the future before final release.
Independent targeting for secondaries
Port/Starboard weapons should be able to fire at the same time if valid targets are present on both sides
Skirmish/Custom Battle mode to test designs
Of those three, what I consider to be the most important is a custom battle mode, but they are all going to be absolutely necessary at one point or another before the game is released.