Game gets stale if you play it too frequently but I constantly find myself wanting to return to it for a game or two. Expansions up the difficulty and help prevent sameness. My rating is with them in mind (it'd be an 8 without them).
Fiddly as heck, but has an amazing feeling of paranoia for uninfected people and stress for the host for the first infection if done right. If people don't really play thematically, it can fall apart a bit.