I will nominate, Twilight Zone as the most modded game of all time, but that's mostly due to longevity.
And from what I can tell, Stern's Godzilla, is making a serious run for the title these days.
Of course with today's modding community standing on each corner, there are a lot of choices.
And for the record, I'm blown away by some of the creativity and talent we have now, but I'm definitely a minimalist.
I remember a time when Cliffy was the only game in town.
Look at what he has inspired.