The nice thing about lisa kudrow is that whenever you see her in an episode of friends you feel that your watching spontaneous natural comedy, and not some already written script.
What also contribute to her talents are her facial expressions that just slay me. In the episode where she is dating the health inspector, and in order to stop him from closing central perk she drinks the old milk and makes a weird face that kills me.
She is also great in the parts were she pretends she doesn't know what is happening, like in the one with the nap partners, she asks rachel to be her maid of honor and rachel realizes that that means pheobe would get to be monica's and pheobe goes "oh!!!" inocently.
Simply she is a natural comedian and I hope i will see her in other roles, as great as Pheobe.