I reccommend trying Pirates & Nomads.
Best with other humans, of course, but you can merge the TDM modpack races in too.
Just use my AI patcher, and until I can update the patcher, you'll have to add energy stream research to phased weapons research calls on the AIs that use 'em.
To maximize the interesting/challenging/fun aspect, play as a Pirate or Nomadic race (medium/small universe, some AI bonus, any amount of racial points) for the first time.
(Be sure to use all the cheap tricks in the book, or the AI's will walk all over you
)
Note: the current AI patcher is not fully compatible with GOLD, but works fine with Classic.