impact of old reviews on new reviews
Welcome to DataScience.SE. Let's see if I've interpreted your question correctly:


  i want to understand impact of previous reviews on current review


Keep track of which reviews a reviewer has read (randomly withhold some if you have to), and use this information together the rating of the new review to create a regressor to estimate the score of a new review given the age and score of selected previous reviews.

You can do similar regressions with the topic and sentiment, if you use embeddings.