I've never really had any serious problems with level-draining creatures in D&D. Granted, it's a very deadly form of attack, but I think there ought to be some very deadly attacks in the game. That said, perhaps under the baleful influence of RuneQuest, I've started to question level-draining on two fronts.
1. On the purely mechanical level, I'm slowly coming round to the point of view of Dan "Delta" Collins that most, if not all, magical effects ought to grant a saving throw. I think saving throws tend to be undervalued in D&D and should be used more broadly. There are plenty "save or die" effects in the game, so why should something like level drain not grant a save as well? I certainly can see arguments against granting one -- and that's how I currently use level drain -- but I'm not convinced that the danger the attack is supposed to have is lessened by the possibility that a character might, with a good enough roll, escape it this time he's struck by a wight.
2. On a naturalist level, what exactly does level drain represent? It's here, actually, where I find the case against the current implementation of the ability to be strongest. I really like the notion that some types of undead are so evil and reality-warping as to be able to wreak devastating damage on their opponents, but level drain seems very mired in game mechanics. No characters in the settings of my campaigns talks about character levels; they're purely a construct of the rules (unlike spell levels, which I at least take to have a meaning within the game world). So, what precisely is it that a level drain is doing within the context of the world? How can you explain it without recourse to the rules?
I don't have any answers to these questions yet, but I'm increasingly leaning toward both allowing a saving throw for level drain and substituting something other than levels for the drain. I don't think this is unwarranted and, done correctly -- permanent hit point or ability score drain, for example -- the effect would be just as deadly and more (potentially) explainable within the context of the setting (Yes, yes, I know hit points are a problematic concept too; I'm just thinking out loud here).
Still, there's also a part of me that rebels against the notion of changing level drain. It's one of the few attacks in D&D that genuinely puts the fear of God into even the most foolhardy players and encourages cleverness to avoid it. I like that and would hate to lose it. But it feels like such a clunky, frame-breaking mechanic that I have find myself wanting to find a way to make it work in ways I find less problematic.
Anyone else have any insights here?