Rapidly refreshing outposts were the primary source of fun to me: the fact that they respawned meant that there was nothing gained by attacking them, it was much more rewarding to plot a route on the map and sneak past.
In fact I normally printed out a map and annotated it with patrol positions to help plan my routes between missions, usually via rivers, quickly fleeing if spotted.
Most of the game for me was an exercise in navigating the map at night (sleeping until night if necessary) and getting into a good sniper position for my next target (being sure to be close enough it wouldn't reset).
I think respawning is justifiable as a mechanic, though it would be better for infinite reinforcements to arrive on an infinite stream of transports. That would probably be too harsh for the people who fight their way through the checkpoints though.