Yes SeAnVeR, we all worry about that. It's a big problem.
There are really two distinct questions here.
1) How do you stop the player from missing cutscenes, screwing up hidden objectives etc?
Here I think it is vital to give clear instructions. It is also important to arrange your triggers and so on so that the game can cope. For example, if there are to be 3 cutscenes in 3 different places in a certain order then the trigger for the first cutscene must have !cutscene2 and !cutscene3. In other words the mission should not advance unless the player follows his instructions.
In extreme circumstances mines and courtmartials are appropriate here, but its much better to have proper things in the game .... for example the truck doesn't unlock until you speak to the sergeant like you have been told to do. If you wanna miss a cutscene and walk to the battle area then you're missing out an important part of the mission, why would a player want do to that? And why, as a mission designer, would you want to stop such an idiot?
2) How do you make the player do what you want in gameplay?
This is really what SeAnVeR is talking about. Given that one of the great strengths of OFP is its flexibility, mines, courtmartials, etc are, IMHO unacceptable and just lazy designing (nothing personal dudes!
). The exception of course is when the CO says "whatever happens don't go east of Morton" and if you do you get zapped. But if the CO or the briefing is going to say that, there better be a good reason for it.
If the player's character has been given orders by his CO, then whether he obeys or disobeys these orders should have consequences in the mission. SeAnVeR's problem, of how to control the player's axis of attack, is a very common one. In certain circumstances its very easy: for example, in a tank mission you have to go between the woods and a few mines or fences soon channel you into the right area. I usually take the view that if the player wants to spend half an hour driving right round the island to avoid those sorts of things that's his funeral. I don't use "death triggers", though I do use hint "You are leaving the mission area". I really don't see why the mission designer should say to the player "No, you can't use that part of the island" without a very sound reason. This choice is one of the game's strengths, why would you want to limit it?
I play like Kali, in that as a matter of course I will always flank an objective rather than approach from the direction of the insertion point. Sometimes it makes a difference, sometimes it doesn't. In this case, SeAnVeR, it should make a huge difference. Tanks and helicopters are crude and unrealistic. What would actually happen? Your orders are to attack the village from a particular angle because your CO thinks that is where the defenses are weakest, or because that's the most favourable direction geographically, or because that's the best way to link in with the other squads, or whatever. So the consequences of disobeying should be appropriate to the cicumstances. You, the mission designer, are the CO. Why do you want the player to attack from that direction? What advantage does it give? How do you represent the removal of that advantage if the player goes in from a different angle?
Winning SeAnVeR's mission by going straight in should be virtually impossible: winning it by going round the flank should present a fun challenge. It's up to the mission designer to ensure that that is what happens. Another strength of the game is that subtle difference of unit placement, weapon loadout etc make huge differences to gameplay. Imagine advancing your squad across 400m of open ground with a few soldiers shooting at you: easy. But against a couple of snipers and a couple of machine gunners? Different story altogether. The mission designer can use this strength of the game to his advantage.
In this particular case I would do something like this.
1) stronger fixed defences on the direct side (better quality soldiers, more strong units like snipers and machine gunners)
2) better placed units: you may even place some deliberatly badly on the flank side
3) add advantages on the flanking side such as camcreated bushes ... or simply choose the flank side such that it offers better lines of sight
4) the other squad will only attack when the player reaches the correct position. If he attacks incorrectly he doesn't get the support of the other squad and if he makes itinto the village from the wrong side he gets a radio message asking what the hell is going on. Or have the other squad move around and also approach from the wrong angle, making it more likely there will be a "blue on blue" and therefore reducing the forces available to repel the inevitable counter attack
5) a little goodie appearing when he reaches the flanking side, like his squad is strengthened by the 2 special ops loons who have been hiding there are observing the village. Or capturing a deserter from the village who gives information on its defences. Or these special ops loons have had an ammo drop and they have one or two nice weapons they can lend you ... you could hear about this via a radio message
6) you can do tricks with the timing of guard groups. Attack from the wrong side and they will come at you all at once: attack from the correct side and they will come at you one at a time.
7) if all else fails and you really can't think of anything else then have slightly more defenders on the direct side
That's 7 ideas off the top of my head, you could think of 7 more ... each one of them would only have to be implemented to a small degree for the overall effect to be decisive. And that's all before you even start thinking about any real scripting.
In summary, a well made mission will make the player "want" to take the correct path. However, it will cope effectively whether he takes the correct path or not, and reward/punish him appropriately.