I got half way through page two before giving up and posting. If this has already been said, it needs repeating.
Any game that allows you to blow up half the flipping planet should have stealth. The major problem with most games is a terrible stealth element. In RF:G, it would be incredible to perform what Yahtzee described. With terrain deformation should naturally come the ability to dig through it undetected. Stuff the headlong assault, I want to plant demo charges on the generators, down the power and kill them Sam Fisher style. Sneaking around guards and setting demo charges along all major paths to make them impassible is something I know woulda helped in the MGS games.
Perhaps the physics engine can be described as a supercar; you're never going to fully exploit its potential. Doing so could ruin your day. The same goes for the geo-mod engine (that's what the original was called, if memory serves); you don't have to perform every mission in a shooty-boomy manner that puts a Die Hard action sequence to shame. The greatest point of a system that allows total destruction is that you don't have to cause total destruction. Wouldn't you feel prouder knowing you've managed to just kill off all the guards in an outpost and set booby traps for the inevitable reinforcements destined to see 'why radio contact has been broken'? Wouldn't you rather perform a precise demolition and watch the engine perform its thankless task of bringing the building down for you?
That's the obligation Volition should have spotted when making RF:G. That you can blow it all to hell and back, but you don't have to. You should have been able to sneak into the base undetected. You should be able to take them out without them ever knowing you're there.
And it should make sense, right? With all the samey shooters nowadays, the lads who made RF:G could have made a stealth system that would rival the system used by MGS4. Then Volition would have nailed it. It could have been the last shooter you'd ever need; the ability to take lots in, give lots out, but not have to be a one-man armageddon. You could try and use stealth, to sneak in, to perform batman-esque takedowns. And if it all goes to hell, you have one very big RPG to take them out with. You could try, in one game, the techniques offered in six or seven different ones. And that would have made RF:G a defining game in the shooter genre; the game that finally got it all right. The game that's as close to FPS heaven as you could get.
And I know such a system is possible; look at what most games nowadays can put out. Look at Arkham Asylum, Mirror's Edge, Prototype, Infamous... They all have good mechanics. Imagine Crysis with a terraforming engine and a decent stealth system. Would that not be one of the best games of all times? And if dealing with slightly inferior graphics is the only real downside, then I say bring it on! There's no sense in polishing up a shit game now, is there?