I turned to CBS because I wanted to watch NCIS and it seemed to be either the only or maybe the best way to watch current CBS shows. CBS has a lot to learn from other TV streaming sites. It is slow and when watching with commercials, it cuts the show up poorly. Hulu has a much cleaner interface that plays much more smoothly and remembers shows watched and where viewing left off. CBS does not provide a very convenient or enjoyable user experience.
So far I have not found a way to identify shows I have watched on CBS All Access. That adds a very annoying waste of time when returning to a series because it forces the need to guess and watch through the first commercial and some of an episode before realizing I already watched that episode, then repeating that until I find the episode at which i left off. The slowness of loading adds waiting time and further diminishes the user experience. I suppose one solution is to keep track in a spreadsheet or some other document I maintain, but that is just another inconvenience.
Another flaw in the site is their choice to put only selected episodes of some shows on the site. This destroys the continuity of a show and diminishes the desire to watch a series. I've found that I will put up with these things for a series that was true long time favorite, but that shortens the list of shows and ultimately, makes paying each month less likely. More likely I will sign up once or maybe twice a year for one month each time and catch up on the top favorites, not watching shows that do not have full seasons available and not checking out much of anything new.
CBS needs to understand the online viewing audience they seek. I'd rate the user experience fair at best and poor much of the time. It is worth the annoyances for specific shows but I will let go of most shows I used to watch and might have watched on CBS.