Haven't read the whole thread, so forgive me if I repeat others' ideas, but I'd like to throw some general ideas out, particularly in regards to those moments that have the greatest potential for excitement: the application of metal and high explosive to targets.
First, for any of these to be "holy sh!t" moments, the developers must first exercise some restraint. If, as in Il-2, every target suffers a catastrophic fate evey time it is destroyed, the potential for surprising moments diminshes with each minute of the game played. Every ship explodes and sinks in a matter of minutes (an exceedingly rare event in real life); every vehicle erupts in a multi-story fireball when straffed; every structure collapses completely when bombed, sometimes when the structure is not even enveloped in the explosion effect of the bomb. Every single target you attack suffers the most dramatic ending possible. The potential for surprise diminishes to zero.
So before I recommend some "oh sh!t" moments, first there needs to be more mundane potential outcomes. Sometimes vehicles should just burn or smoke, not explode. Sometimes structures should only suffer partial damage, perhaps just a hole or a collapsed wall, and there should always be dust/debris, but not necessarily fire. Ships should typically just burn and/or list while slowly sinking over the course of hours.
With that, here are some truly dramatic moments that could occur:
-If a train engine or steamship is struck with AP rounds or penetrating bomb, there should be a chance of a boiler explosion with attendant column of steam rocketing into the air.
-If a steel/concrete bridge is bombed, there should be only a small chance that an entire span will be dropped (when it happens it would be very dramatic).
-If a train car, truck or ship is carrying ammunition, there should be a chance that attack will result in an enormous and very violent explosion (see 0:54 here:
). However, not every vehicle, train car or ship should act as if they are carrying ammunition.
-Likewise, there should be ammo dump or bunker structures with the same potential for catastrophic destruction.
-Flak and other infantry-served weapons on the ground should seldom explode. An explosion should be a surprising event. More typically, flak should simply be supressed (temporarily or permanently abandoned/unmanned).
-If a ship has a torpedo detonate underneath the middle of the hull, there should be a chance for the ship's back to break and split into two.
-A tank should only explode if its ammunition ignites, which should be a violent event with fire shooting out hatches or the turret displacing. Otherwise a tank should simply burn or be abandoned.
-parked aircraft should not have on/off damage models and should not typically explode.
-Not just armor, but most surfaces, including metal aircraft skin, should offer a chance of projectile deflection.
-damage to the bridge of a ship should potentially cause the ship to lose command (stop maneuvering, return fire less effectively); damage to the engine room or propellors should potentially cause loss of propulsion.
-In general, different fusing of bombs/rockets should result in a greater variety of outcomes on the target and "hit point" damage models should be abandoned wherever possible).