I think the new Chaingunner is quite badass
. As far as Sarge goes, his head is good but his boots match his hair; therefore he looks as if he's wearing a helmet from behind. Perhaps chaning the color of the boots to the more Doomish khaki color might help?
As for the Alien, I can easily add fangs. He
will have an elongated head, but that's not visible from the front view.
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EDIT:
About an hour or so later... Might I add this is possibly the most legit Alien sprite I've seen for Doom. Just sayin'.
And please don't make jokes about that thing between his legs (during the attack frames). It's a tail, m'kay?