Save or die effects are really easy to abuse offensively (as a player) and they require either luck or hard counters to defend against as a player -- neither of which are very interesting, tactically.
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Hard counters in a single-player RPG are obnoxious, IMO because either you're prepped for them or you aren't. If you aren't, you reload and voila, you are. If you prepared save-or-die tactic that the enemy is immune to, you're hard countered through no fault of your own. If not, you steamroll the enemy. Or you do what many players do, which is reload until the primary target fails its save and the entire tactical challenge of the fight is rendered trivial/pointless.
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I believe this does make the game better. It's not second-guessing; it's simple observation. If players can use save-or-die effects against an enemy as a tactic that has a 10% chance of success, many would rather reload repeatedly until the target drops than develop adaptive tactics to deal with the specific threats posed by the enemy. Why should a player bother attempting to adapt when they have a big hammer with a 10% chance of ending the fight each time it's swung? We give them the tools. But we don't have to include save-or-die effects, and the game isn't made worse by doing so, IMO. Luck is an element of conflict resolution, but the larger element in A/D&D as levels rise is, of course, BONUSES. In 3E/3.5, saves progress in such a way that at higher levels, many classes have virtually no hope of making saves against their weak save categories and it can be extremely difficult to shore up against the numerical disadvantage. When the effect is a save-or-die (or equivalent), it can immediately remove the character from combat. If the saves are hopelessly improbable, the solution becomes a hard counter (like Death Ward) which typically relies on post-reload metagaming to make the deadly effect completely impotent. Even in tabletop, where reload is not an option, the virtual absence of save-or-die effects from 4E was never missed by our gaming groups in over 2 years of play and two different campaigns (albeit one much longer than the other).