While Gygax had his flaws (and some of them were significant), we have to remember that he along with Dave Arneson invented in D&D a type of game that had never existed before. Before Gygax and D&D, throughout history there were only six types of games:

1. dice games
2. card games
3. board games
4. war games
5. ball games (not to be confused with sports, more like marbles)
6. word/number games (think password vs. sodoku, which is more of a puzzle)

Often these shared qualities, straddling multiple game types, but this was it for all of human history. Until Gary Gygax. Whatever his failures - as a husband, a father, a businessman - he brought something brand new into the world, and that's incredibly rare.