I believe I know the set you're talking about--it was produced by WotC in 1998 or 1999, and reused the art from DLQ1 Knight's Sword for the cover. Unfortunately, tracking down more details is providing a challenge ...
EDIT: And LordBP's link comes to the rescue! It sounds like the D&D Adventure...
I stand corrected; I haven't touched the War of Souls since release, save for a brief skim of an Advanced Reader Copy of DoaVM to see what had changed between it and the final version.
You can't decapitate yourself by default with a fumble in either RM2 or RMSS Arms Law. To get a death result, you'd have to
roll a fumble;
roll a natural 100 on the fumble table while using a one-handed, mounted, or thrown weapon, which triggers a "D" level critical of varying types
roll 86+...
Anything that's not some form of D&D? :) A bit tautological, yes, but the game has always had certain strong flavors built into it that channel it in certain directions. What those flavors are change from edition to edition, but it's never (with the possible exceptions of OD&D, which was little...
D&D can't handle Biblically/theologically accurate (that is, realistic) angels and demons. The system breaks down for those levels of power and intelligence.
The 3E sorcerer, the Greyhawk thief ... possibly the UA cavalier, although that wound up removed from the game. I don't recall the 3.5 warlock catching quite so much flack.
(And the 4E warlord is obviously the one you think people are thinking of. :) )
There have been two strains in D&D from nearly the beginning--"D&D as fantasy toolkit" and "D&D as unique game experience."
Appendix N can be useful for both, but its usefulness to the latter is primarily in identifying the sources that create the "D&D flavor." Since WotC is thoroughly...