As Sisko said, it's easy to act like a saint in paradise. Out in the frontier, tough choices have to be made and the heroes are more flawed.
A far more realistic view of space exploration than Roddenberry's.
I have to say that I believe seasons 5-7 to be the pinnacle of Star Trek story-telling. I loved the mythology they created and how the show left me satisfied and wanting more all at the same time.
Eh, Seasons 3 and 4 are a lot better than Season 7. What You Leave Behind did a great job at wrapping things up though and is the best Trek finale.