The High Frontier second expansion is feeling that way to me (though no wargame).
I'm going to play an HF scenario to catch back up on the core rules to get to where I can tackle it though.
Colonization's biggest annoyance to me is wrapping my head around all the new stacks and tracking where exactly the hell they go. Most of that had to do with the out-of-the-box rulebook being a maze of particulars that had to be cross-referenced with the original rules to see what changed.
The living rules and a few extra markers made the game far less daunting.
EDIT: Well crap I forgot to bother answering the topic's question. Next War: Korea is currently being a real uphill struggle, mostly because of the amount of printouts of errata and living rules it's demanding. It's also a game I'm having a hard time visualizing the play and compartmentalizing mentally. That SoP goes on forever.