I like Alyx and think she works for these reasons:
1. She gets scared
2. Her relationship with her father makes her motives understandable. He is a good man, they only really have one another now.
3. She's the daughter of two scientists and Dr Kleiner's honorary niece, it's no surprise that she's good with technology;
4. Her stilted flirting with Gordon is really quite cute and endearing because it's awkward and innocent, and only sprinkled in the game;
5. She shows genuine fear when facing up to the Hunters after the Vorts save her from dying;
6. It makes sense that she's an action-girl because she's spent almost her whole life figuring the Combine. It's like all the French women who were part of La Résistance in WW2
7. She has her moments, but never takes the spotlight away from Gordon (the player).
8. Her skin colour plays zero part in her character story, this is an example of good videogame character writing which you don't see in current year. It's never mentioned:
9. She is lithe and small, she is a woman, it makes sense that she is acrobatic and can get into places a bulkier man could not.
10. She's pleasant to look at, excellent waifu material. I hope HL3 ends with her and Gordon raising a brood of absolute Gigachads and Gigastacies while the Cuckbine seethe and cope from their gay universe.