I received an email asking me why I was continuing to run TSR editions and retroclones instead of just using 5e. Since the D&D 5e Player's Handbook was released last summer, I've had the occasional request to review 5e. Although I have the three core books and have read them, I've refrained from doing so because I just don't care enough about 5e one way or the other to write a good review. I've discovered over the years that if I don't really love something or really hate something, any review I might write of the game is going to be boring and not all that useful.
Telling people that something is "okay" or "downright average" really doesn't help anyone decide whether or not to buy it and there have been so many reviews of 5e that I really don't think anything I could say would be worth reading. However J. wasn't asking for a review, he was asking a much more interesting question -- or at least more interesting to me -- why don't I use 5e to run my games?
While I think D&D 5e is an okay game that I would be happy to play a character for in a campaign with the right group (a first for WOTC editions of D&D), it's simply not a game I want to DM. There are several reasons:
First, I run campaign settings designed for TSR editions of D&D. Changes to D&D that others might consider positive can be huge negatives for me. For example, a Sleep spell that lasts only one minute (instead of the hour or two it would usually last in TSR D&D) or a Charm person that lasts only an 1 hour (instead of the days it would last on the average person in earlier editions) simply makes some of the history and background of my settings impossible. I have no desire to rework the background of my settings or tricks and traps in dungeons to handle 5e's nerfed spells (and other seemingly minor changes) would cause.
Second: the Advantage/Disadvantage system. I know many people just love this system, but I'm not one of them. It seems to be overkill to solve the 3e/4e problem of people spending lots of time hunting for one more modifier. As I don't have min-maxers or rules lawyers in my games, this is simply a problem I've never had so I don't see much reason to replace modifiers with a system where only one modifier can apply and no matter how many positive advantages an action has, one disadvantage trumps them. This just seems to be too blunt of an instrument for the "modifier hunt" problem. In spite of my dislike for the advantage/disadvantage system, as a player I can live with it. As a DM, I can't. Many times I'm dealing with ten, twenty, thirty or more orcs, goblins, or whatever in a combat. With a modifier based system, I can roll 5 or 10 dice at time (handling the attacks of 5 or 10 monsters), eyeball the modifiers, discard the misses and roll the damage for the successes. With the advantage/disadvantage system, however, the minute the monsters have advantage or disadvantage, I have to roll two dice for each monster separately which greatly slows things down. I discovered this back in the 1980s when I tried a version of this system. Sure, I could redo all the encounters in my dungeons and wilderness areas replacing masses of low level creatures with two or three higher level ones but that would be a lot of needless work and would not even make sense in world in most cases.
Third, character creation takes too long for my games, has too many options, and requires more time and effort than I want to have to devote to it, especially with the new and/or casual players that my games attract. I realize that all the options make many players and GMs happy. I'm just not one of them. I also do not like the advancement system which blows through levels (especially lower levels) far too fast for my campaigns and has attributes inflating rapidly with levels -- especially if you opt not to use feats. Attributes are more important in 5e than I like in general.
There are a good number of other nitpicks that keep me from using D&D 5e to run my games, but the above three are the major ones. Sure, all of these issues could be worked around or I could toss out all my work and design settings specifically for D&D 5e. However, given that TSR D&D rules still exist (and with all the retroclones aren't going away) and still work just fine with all the setting material I developed in the 1970s and 1980s and still use today, there's really no rational reason for me to do so. 5e wouldn't bring anything to my table that would be worth all of the extra effort. Of course, this does not mean 5e is a bad game, it just means that 5e is not the best choice for running my campaigns.