Of course I like modrons. In Monster Manual II they were silly-looking geometric shapes with legs, but for Planescape they were redesigned by my favorite artist to include steampunky clockwork elements. They were still silly looking, of course, but in a good quirky way.
The first chapter of The Great Modron March was the last Planescape adventure I ran. After that, 3rd Edition came out and the modrons were no longer the primary inhabitants of Mechanus, being replaced by centaur ants and robotic giants. The boringifying of D&D’s monsters began there, and continues to this day.