The most frustrating thing I've noticed in a few games I've been playing through recently (namely Far Cry 2 and Mercenaries 2) is the ability of the character to be forcibly or unintentionally trapped within the confines of a large, empty boulder.  This has happened to me on multiple occasions in each game, with my most recent entrapment costing me no less than 2 and a half hours of gameplay loss.  I was simply playing Far Cry 2, on my way to a save point, when I got downed.  Luckily for me, I had an ally on "rescue-ready" who came to bring me back to life, right?  The only problem is that the ally somehow decided it would be a good idea to drag me inside of a large rock (hollow on the inside, nice job Crytek) with no way out.  Thus, I was forced to backtrack through what was already tedious diamond-finding the first time through again.  Not only can the player be trapped inside of rocks in these games, but so can enemies.  And from what I've seen, these rocks provide the perfect shelter, bullet-proof on the outside, yet completely bullet and grenade permeable from within.  Enemies trapped inside will continue to pick you off while you scratch your head looking for where the indicator is pointing you.  In Mercenaries 2, often the enemy within the rock was the one who would call for reinforcements, which presents its own problems.  I don't really have a solution for this problem, other than perhaps to not take the easy way out and actually make solid rocks so collision-detection can catch this sort of thing, but in 2009 should people really be losing their progress because they get sim-syndromed (no doors out) by the developers?