I have done some Spartan Races. They are fun but also tough. I would also suggest the Metro Dash races. They are much shorter that Spartan or Tough Mudder races but very intense. They were developed by Navy SEALS.
They are derived from the military style boot camp exercises and are much more enjoyable when you don’t have a drill sergeant yelling at you. One of the best things is the team building and camaraderie that comes from completing the event.