I like her, but she never really clicked in the Avengers. Although that being said, she clicked better in the Avengers than anywhere else. Since the question is Jocasta as an Avenger, I'd rate her about 3 out of 10. Better than the likes of Deathcry and D-Man, but definitely not even close to top tier.
My favorite use of Jocasta was as Pym's weird love interest in Slott's Mighty Avengers run. She was created using Jan's brain engrams, so they made a bit of sense, but were considerably creepy too.