Conveniently Indestructable Objects
This difference between this cliche and the previous one is typically a matter of degree. The previous example refers to short scripted events while UGS (Unbreakable Glass Syndrome) tends to occur during plot sequences. One moment, you're walking through the game world carrying enough weaponry to devastate a mid-sized country. Suddenly, you catch sight of something important. You race forward, only to come up short against a pane of glass or other barrier.
You can tell this is an important plot sequence because I'm standing there like a moron.
To add insult to injury, the main character will often hammer on it. With a fist. As opposed to the FleshRend 9000 or Phase Transition Cannon strapped across his back. Avoiding this trend is more about good storytelling and scene creation than anything else -- giving players reasons not to do things is a much better way to handle the situation than arbitrarily forbidding them from doing so. In a game like Dead Space, pictured above, the reason could've been the risk of vacuum exposure or the high likelihood of killing the two hostages. Instead the doors are conveniently locked and none of my weapons even scorch the paint.
Monsters can smash through whenever it's convenient.
In this case, right after killing my captain. I stoically watched.
Ideally, let's just get rid of invulnerable structures, period. No more chain-link fence that moonlights as a solid surface, no more flimsy wooden doors capable of withstanding tank fire. A few games, like the Red Faction series, have played with this -- DICE has the right idea with Battlefield 3, which allows for a significant amount of environmental destruction, but such titles are a distinct minority.
Giving players the freedom to re-shape terrain does create certain challenges, but not as many as you might think. There's a reason why soldiers in the real world don't go around firing rocket launchers inside of buildings or hurling blocks of C4 at the opposing side.
Not Pictured: The original building
Physics, it turns out, is a really nasty end boss. The over-enthusiastic use of explosive ordinance in confined spaces could kill innocents, destroy valuable upgrades and ammo, completely ruins any chance of a stealth mission, and creates clouds of dust that choke and blind a player. At the same time, destructible environments open up more avenues for players to experiment and have fun inside the game.