I think your female characters look pretty good, but I wonder if it's just that they all have distinctive hairstyles. All the dudes look more or less the same. I think if you could find a way to characterize each person, they would read more like different characters. (This is especially true of the TOS crew. The the other crews have more gimmicks, like aliens and bald guys, but still...)Right now, they all basically have he same features. Try mixing it up with the jaw line and proportions. It can be tough when you are married to some particular style (in this case your take on anime). But look at most professionally designed characters and you'll see that the different characters are different enough to be distinguishable in just the uncolored line art of their heads.
Like I said, your girls are really good, but I'd like to see more variation on the guy's features.