They haven't gotten a lot of love lately. I think quite a few aspects need to be reworked. I really would like to see no autonomous use of alien powers, especially mind erase. I think that any moodlets related to aliens should be rewritten. They're dealing with their own kind. I also find it weird that creating a married couple that are both aliens still "discover" that they are both alien. If your sim is an alien and knows aliens, they are more likely to get abducted. It doesn't sit right.
Sorry if I don't sound very eloquent. I'm not very good at writing down my thoughts.