(Maybe this thread belongs in the DOS talk forum?)
Anyway, to answer your question, one obvious answer is Master of Orion or MOO2. Randomly generated maps, tons of different options and variables for each game and endless play styles – pretty much the perfect recipe for replayability.
You mentioned level editors, so it’s also hard to go past Duke3D. I almost certainly spent more time in my youth making levels than playing the official episodes.
It also depends on what you mean by replayability. There’s a number of games I come back to nearly every year even though there’s nothing really new to discover. (I’m replaying Hexen right now in fact!)
Some games just have amazing atmosphere or fun mechanics or some other mysterious x factor that makes them a joy to revisit time and time again.
But I guess for most people “replayability” means not needing a cool-off period – just keep playing them non-stop for an indefinite amount of time. In which case any game that’s good for speedrunning is a contender, and you will often get an active community to boot.
Apart from Doom, however, I can’t think of many DOS games that have a particularly large speedrunning scene (but I also haven’t looked into it in a while)