I have downloaded and played several good SP missions.
However, it seems that the intel is always pretty good, ie: your objective is really what they say it is, in the right place, etc.
A whole mission can revolve around bad intel. For example, I'm working on a mission now where an early morning raid by a Blackops team infiltrates through patrols leads the player's group through several stages where the intel is dead on, like supply stashes, suspected enemy positions, etc, but when they reach the town where the tanks are supposed to be, they are all hidden under camo netting and vegetation. When you get close enough to set a charge, you trip a trigger that tells you (if you hadn't already noticed), "these tanks are made of rubber and wood!" or "this tank is a decoy!"- they are all simply armored targets. Suddenly, the primary objective is God-knows-where, enemy patrols are still out there, and if you investigate further, the camp where the 'tanks' were supposed to be is really a secondary target: a well defended and hidden Shilka that has been shooting down NATO transport planes. Trouble is: blowing the Shilka up first causes problems- the mission still needs to be done in order of primary then secondary target, just so you survive- atract attention to yourself too soon and you've had it.
Another idea is to have an objective's intel right on, but- the location has moved several kilometers away, such as the Scuds you were after moved over the hill at the last moment- now you have no tactical plan- you planned the attack for the valley you're in now- which is deserted. Your team now has to alter it's plan quick to destroy the Scuds.
Even a straightforward 'clear the town' scenario is more tense if nobody's home....there's the trucks and transport, and the defenses...a couple guards-but were are the bulk of the enemy troops? Where'd they go, and- when will they be back, and from which direction?
It's that much more exciting when you find out that your neat little sabotage mission, or your routine attack on a presumed enemy held town is 100% out of your control after all your careful planning and recon. I like low-light condition, like dawn, so your eyesight is compromised, but enemies with IR goggles can still use them. I also like making the best approach to the objective the one that puts the sun in yours eyes, so even a simple advance into an 'unoccupied' town is flying blind. Two enemies behind a low wall can put a damper on your stealthy appraoch real quick if you never see them.