The full grand campaign in War in the Pacific: Admiral's Edition.

Ypu fight the entire Pacific War in 3 day turns across a map with 40 nautical mile hexes with the full order of battle at your disposal. If you play seriously to win against a capable opponent, you have to manage everything right down to individual pilots. There are thousands of ships, thousands of planes and pilots, and hundreds of land units. It is almost more of a historical achievement than a "game". You can play against the AI, but the real experience is to play against another person by email. The full campaign could take 450 turns if you play it out right to the end. Of course, one side can concede early if defeat becomes inevitable, but even so, if each player takes one turn per day, it will probably take about a year to finish. And you won't just be spending time taking your turn, you'll also be reading up on the actual war strategies of each nation, analyzing your opponents moves, planning your own moves and strategies, figuring out supply logistics, learning the capabilities of the ships and planes at your disposal, reading intel reports, and managing virtual pilots and commanders. In many ways, WITP:AE is more of a technical and historical achievement than a game. I honestly don't know if I'll ever be able to complete the full campaign. I would certainly have to be retired before I'd ever attempt it versus a human opponent. And even if I could fully commit, who knows if my opponent would also have the fortitude to finish.