I think it should be very rare. For example, if you drop in one hit, then there should be a buffer of negative HP, death saves, or something else.Do you want "low likelyhood" or "not possible at all"? I can name a number of games for the former, but the latter is a smaller list.
Some special maneuvers are okay. But I'm also thinking about flanking, attacks of opportunity, retreating.As in "Trip, disarm and other special manuevers" or "the above plus combat tradeoffs?"
I want them to be able to learn how to play without taking home a 300+ page rulebook and studying it for weeks like homework.This one is hard to answer because where I come from I don't consider anything in the D&D sphere as easy to learn, wheras I consider some other games a lot of people claim are difficult relatively easy. (I also don't think most simple games tend to fit your second requirement up above).
Yeah. It's sort of you just throw stuff and kill characters until you can figure out what the characters can handle - until those characters are replaced (or get more abilities, better equipment, etc.) I feel like that should be a pretty major part of any game design, but it's often not even given a second's thought - which is a shame. It's the main reason my groups fall off systems.Tell you the truth; decent encounter building tools are, on the whole, rare as hen's teeth. I can think of one non-D&D sphere game that has one, but it probably fails your "Easy to learn" criterion.