Before You Watch
Most movies and series produced by the motif of time travelling are boring, complicated and difficult to follow with. Outlander is not one of them. The time traveling has appears in a few episodes but disappear in a way that everyone forgets that a character comes from 200 years later. You watch a historical story most of the time, especially in seasons 1 and 2.
After You Watched
Outlander has several great episodes in the 1st season and Claire as someone from future plays a significant role in the story but like many other TV series, Outlander starts to degrade to an ordinary drama and many sex scenes for Caitriona Balfe who plays as Claire.
Unlike other fiction stories about time travelling, Claire adapts herself to the lifestyle of 200 years ago and after 1st season, she looks like someone from the same era. Not only she is not surprised by anything in the past, but her presence also looks very normal to others.
On the other hand, Outlander attempts to tell its story parallel to the history of Scotland in the season 1, but gradually gets away from the historical facts and even ignore details of the events. For example, when Jamie and Claire should be poor and in a low level of life, suddenly they appear in luxury costumes and even Claire can enter the French court and meet King Louis XV of France.
Besides these flaws, Outlander is still a successful series that can get its viewers to watch all the way until the end of every season.