The lack of graduation due to difficulty settings is yet another obvious bug, but the game really isn't as bad as a lot of people are making it out. You really need to start over in a new game to appropriately play through the new economic settings -- all of your decisions in past savegames were predicated on a completely different set of assumptions and expectations about what you could do at any given level of expansion.

Restarting my Prussian campaign, in which I'd previously conquered Africa with pikemen just for something to do, just prior to my first landing in Morocco resulted in a massive change in events -- none of the factions I'd been sending money to so they would even field troops could support their armies and it was absolute pandemonium for a few turns. And for a change, it was fun.