it's great
We do this in our games and it's awesome. It leads to tons of unexpected events/scenarios, etc.
We use a modified item/structure save system than core, and I will most likely move the same system to 4E. Due to this, I always check for damage to structures, or natural environment, items, etc.
From one adventure, that my friends completed back in about march, let's just say some of the terrain/structural events that occurred in that one adventure.
Setting: 'the complex', a 90% underground, huge 'scientific/magical' research facility; players woke up as prisoners and had to escape.... over 20 levels down, fully 3D mapped, and tons of freedom in that players could have escaped via climbing up some shafts they found, but due to some excellent roleplaying (by a charmed individual, he was able to convince, not via dice rolls, but actual roleplaying/acting, for everyone to descend further).
* critical explosion, as the party tried to turn off a magical machine...with energy being funneled through it. THey opened and released some energy without actually shutting the flow first (through the focus which was a captured demon); I rolled for it, and failed...the energy tore through the outer shell piping, through the inner shell, out into the rest of the complex. the release caused a critical explosion and caused a temporary black hole type effect below them. They ran before this, but caused the entire center column to collapse into the 'gate'. I then had to estimate how the dungeon change. It got pulled into this gravity well, and entire levels of it collapsed or was bent in, metal piping bent, bricks shattered, etc. after that, rest ofthe place was going through a wrecked complex with tons more hazards
* due to a villain there, who had some..random effects...a wild psion type, who couldn't control powers, when injured, i rolled to see if she could control her anger, if not, soemthing happened as she lost it, and unleashed energy (similar to that of an alter reality/wish/reality revision effect). THing was, her group was below the players in the complex, so i was rolling for the rooms they completed, and where they went, so stuff was happened that they ddin't understand, due to her doing her own thing as well.
WHen she lost it, several stuff happened:
* she turned about 5% of the complex temporarily to ice. I had to then figure out what happens to structures that wouldn't be able to handle being turned toice (ie. mechanical featuers like gears for example.
* later, she caused about 25% of the complex to turn into water. everything...water. the party was in this huge arboream type chamber, and suddently, the walls, cieling, most of the plants, floors, etc all turned. They then fell 100 feet down into a sudden ocean of water into the lower levels (bypassing alot actually, but this was not planned...it was fully random from her wild power, so it was fun)...I then had to figure out, how the above levels came crashing down on them,etc. and that was a very tense 3 or so hours of gameplay
* the party ended using a disintegrate scroll to blow a hole in a pipe, to cause water to flow in..this flooded a chamber where the final battle was happening.
* however, at that time, her random power kicked in causing temp to drop, causing much of the water to freeze... so there was a frozen ocean in a huge chamber, with some of the party trapped
* then it got bad!!! another random effect, as ice started to break, a tornado formed inside...it broke the ice and made an ice twister inside, 4000 ft below the ground inside the complex, and began ripping thru the ceiling, etc.
* players began retreating..they said screw the battle
* they got to an escape tunnel and started using items/spelsl to climb up...as they did, the level below turned to slime...and there was an explosion inside. they have no idea what happened..
* above, on the surface, they found under snow/ice where a large section collapsed due to what happened below while they were down there.
* before escaping the mountains, they also were part of an avalanche (caused by a hunting white dragon)
some smart thinking there gave some of the players alot of exp.
As a note, teh wild psion i made, that couldn't control her power, causing all sorts of stuff to happen, I named her "Satya". Same name my wife wants to use in the future if we have a daughter.
Satya, is Sanskrit for "Reality". I named her that, since her wild powers, could cause reality to be altered.
From the above, I fully support anything that makes more sturctured rules for environment alteration
Sanjay