Eloise is 100% a ridiculous Mary Sue, and so is the character of Machiko Noguchi past the original AVP.
And Herk Mondo is a Gary Stue, but a intentional one.
The Alien/AVP EU's got a lot of trash, such as Xenogenesis, DOTS, Colonial Marines, but most of the time even the trashy stuff is enjoyable on it's own merit and the mediocre entries just don't tonally suit the universe ultimately (compromised by one or more outlier concepts) the latest amongst;
The Rage War, OotS/RoP/SoS,
Fire & Stone/Life & Death.
But the real good stuff, such as Isolation, Salvation, Sacrifice, Survival, Wraith, Glass Corridor, Alchemy, Labyrinth, Infestation, Dead Orbit, Dust To Dust, The Original AVP, Monolith's AVP and The Cold Forge.
Means it's worthwhile wading through.