Please be as specific as possible when letting us know what is missing or incorrect. For example, say "this game's trophy difficulty should be 8/10", with a link to a website corroborating this difficulty estimate (if possible), not "this game's trophy difficulty is wrong".
Other than the various subspecies of the invasion creatures which you've met in the high level missions of the main game, you will also see aliens with different arms and weapons as well. Challenge the 10+ ultra hard missions and show off the guts of us human beings. In the ultra hard missions, there appear 30+ new weapons and arms which make the missions a bit easy to accomplish.