Frankly when 7 was first introduced I was less than impressed on multiple fronts. (Oh great she's tall, she's blonde, and she has a rack you could hang coats from, well I'm sure she was cast for her acting talents. Oh and she totally represses all her emotions, well that's not deriviative.) But then two very important episodes changed my opinion forever.
The first was Drone. It's an incredible episode. And by the time it gets to the end where One is sacrificing his life for the good of Voyager and they reprise the dialogue from earlier in the episode I'm dripping tears. Ryan's acting is both emotive and subtle at the same time and that's damned hard to pull off.
Then came Infinite Regress. Watching Ryan switch (often rapidly) between persona's was incredible. But what really did it for me was when she was the Ferengi. She got it, the body posture, the vocal inflections.
After that I was a fan of both the actor and the character.