It's still decent. But the truly interesting thing is always going to be the rise to power. So it should end with him becoming president.
Frankly for a TV show his role as majority whip was probably the most fascinating.
Yep. The first season was the best. The second started out incredibly strong and then waned. The third completely lost its way. Once he was president, it was like they were inventing personal stories rather than playing to the broader theme of Washington power... which meant it could have been a show about a lot of power couples.
This is the risk of audience expectation, however. While there are exceptions like
Breaking Bad that took several seasons for a metamorphosis, I get the sense that writers now are encouraged to accelerate plotlines faster than they would have a decade or two ago. This makes shows risk jumping the shark a lot sooner.