I ran the Tough Mudder in NorCal last October and it wasn't nearly as strenuous as I thought except for the altitude.
The courses are typically built around a ski resort so it has epic climbs up black diamond runs but I never saw anyone actually running those- it became hiking. Lots of the obstacles are fun but not really challenging like going through a tube or over massive cable spools. The only ones that were really mentally challenging were the water obstacles. For NorCal the water obstacles were in the snow making pool so the temp sucked the breath out of you.
Hopefully Tough Mudder got better at this but there was a line at some obstacles so it didn't really feel like a real 10 miler.
In the end though, it is a fun race and the high drop out rate is mainly because lots of deconditioned people attempt it. I recommend it for a fun time.