This is the post I should have written about the Rust Monster. Reading a comment by Chgowiz that he left at the Gamer Dome last month made me realise that I am too forceful when I write about 4e. I tend to write in reaction to the most inflammatory and content-free boosters of 4e rather than the reasonable, even-keeled players of the latest edition of D&D; unsurprisingly my own writing on the subject reflects that inflammatory rancor. It feels justified when compared to the bile-spewing commentors and bloggers, but it's petty and childish when measured by the standard set by the more gracious bloggers. Besides which, swilling that venom for the amount of time it takes to write a blog post can't be good for my well-being.
I'm going to try for analysis instead of trying to viciously savage 4e as if it kicked my dog. (Feedback on where I fail or succeed is welcome.) This won't be opinion-free, because the reason to analyse 4e is to better understand why I like the games that I do and what about 4e makes it not a game I like.
The version of the Rust Monster in 4e is a significant divergence, mechanically, from earlier versions. This is largely because there is no niche within 4e that the old Rust Monster could usefully fill. The way that the creature was rewritten reveals something about the design space that 4e has delimited. Certain things that existed in previous versions simply don't fall within those borders anymore; because the Rust Monster had to be brought from outside the design space to inside, how it has changed in the process reflects the borders of that design space.
In 3e and earlier, the Rust Monster represented a certain amount of risk. It's mere existence in the Monster Manual put characters at risk of losing good magic items since it could ambush them at any moment. If the DM wasn't a dick and used the Rust Monster in a way that made it a clear danger that could be engaged or not, it still presented a risk: give up on whatever the the Rust Monster is blocking or risk having your precious stuff eaten.
4e's Rust Monster eliminates its role as a source of risk. It's a specialised debuff that only works on PCs already benefitting from certain kinds of buffs. Its mere existence in the game canon presents no more risk than any other creature that can temporarily reduce the effectiveness of the PCs. Actually encountering a Rust Monster is not so much a threat as it once was. Fleeing is certainly not going to be the first and smartest choice in 4e. In fact, if there is an item that a PC wants to disenchant, there's incentive for engaging the Rust Monster in combat and deliberately getting that item eaten.
I'm going to go out on a limb and say that this does not make the Rust Monster a risk. Certainly there is some risk, but it's only the risk of a temporary debuff, which is a run-of-the-mill thing in 4e. Comparing that Rust Monster to previous versions, I'm going to call a temporary debuff no risk at all.
For how I want to play, risk is a necessary ingredient. Risk provides the opportunity to make meaningful choices that distinguish one character from the next. There are other kinds of choices in 4e, especially in character building and optimisation, but those sub-games aren't why I play roleplaying games. Those choices don't reveal anything about the character, just about the player. What is this character willing to risk, to get what they want? What ideals do they (or don't they) choose to fight for? What do they fear so much that flight is the only reasonable course of action? Are they willing to risk the Winged Plate of Acoden meeting an ignoble end in the belly of a Rust Monster in order to pursue their destiny like a hero? Or will they run like a mercenary? Are they willing to backtrack, stash their metal equipment in another room, and risk meeting something nastier than a Rust Monster or having their gear discovered by enemies before they reclaim it?
Risk also makes rewards meaningful. Part of what doesn't suit me about 4e is that reward is assumed. A PC is owed rewards for the mere fact of surviving. They don't have to make good decisions, take risks for a chance to get lucky, explore beyond the obvious, or try clever things. As long as they find and kill badguys, the treasure will be placed in front of them where they can't miss it. "Reward" that is guaranteed, that is not earned, is no longer a reward for anything.
The Rust Monster is another expression of this philosophy that treasure is a right for adventurers, not something that is earned. The old Rust Monster made sense in 2e and earlier because treasure wasn't a right, but something earned by playing a smart adventurer and as easily lost through poor play. 3e was an interesting wrinkle by that measure. It retained the idea of rewards being something earned, given that there were nasty Rust Monsters and that it was possible to "miss" finding all the treasure, but also assumed that the PCs would have access to a certain amount of magical items according to their level. 3e was really a hybrid game, harking back to its roots in AD&D but also foreshadowing what was to come in 4e.
In the end, risk-free entertainment isn't something I'm interested in. I don't think it makes for a very good roleplaying game, although I can see how it can be straight-up entertaining in its own right. There's a certain amount of sense to the idea that it's not fun to have your vehicle for enjoying the game seriously hampered, but that does assume that the audience isn't interested in choices and consequences, just the raw entertainment of following a hero with a manifest destiny. I prefer that my choices make a difference in the destiny of my characters, for good or ill. That is what I find entertaining.