Artemkill creeps for 15 minutes
It depends on the game, but high level teams dont seem to just leave the lanes alone until each side can get some farm. I think dota does a pretty good job of rewarding aggression, especially as the game drags on.
But yes, there are portions of the game that are just farming, and those are boring as fuck. Just how stalemating and building uber in tf2 are kind of boring to sit through.
The funnest games to watch are when a team tries to employ a risky or unusual strategy or draft.