Disclaimer: I am biased.
After binge watcvhing the whole show i really have to say that, while the show starts to go downhill after season two (in terms of quality) it really starts to noticeably worsen beginning with season 5. Its not the worst season out there (the last two are definitely the worst in my opinion) but Season 5 set the stage for the flop to the finish line. I would recommend watching it (because you have at least seen season 1-4 at this point im assuming), but only if you can get it cheap (or free). The quality is nice, the blu ray is great. Just go into the last half of the show with low expectations and you should enjoy it!