It's funny that some see the show as a before angels (seasons one to three) and after angels (I guess as there were only fans of Sam and Dean (J2) and the fandom was 'whole' whereas when the angel storyline came in season four, with Misha as Castiel and suddenly people were shipping Dean and Cas together (!)

I see season four as my fave, because the storyline was tight and the acting and writing really amped up, and it was all things epic. Season five capped off that arc in a great way.

In seasons six and seven there was a new showrunner who experimented with different things and the execution was sketchy, but right now in season eight, then went back to the runner from seasons three four and five, and so far, it's been a really good season.

But you could watch seasons 1-3 and skip the angels entirely.