Jennifer Aniston is a popular actress but not an especially successful one on the big screen. A cursory look at her page on Rotten Tomatoes shows many more green splats than red tomatoes*.

The Good Girl is indeed an example of her doing a great dreamatic job, Office Space is a comedy and Cake is a bust though some critics have lauded her performance.

So there is truth in your assertion.

Question: Is Jennifer Aniston's dramatic work underappreciated, as she demonstrated in such films as "Cake", "Office Space" and "The Good Girl"?

For those not familiar with Rotten Tomatoes it is a movie review aggregator that compiles reviews made by many critics and and gives the percentage of positive reviews. Movies with less than 60% positive reviews are referred to as rotten and are listed with a green splat icon while those above get the fresh mention and a red tomatoe icon.