Úmarth
Megalomaniac
Yeah I think my #1 priority tweak for Civ 5 would be to have somewhere -- cities, forts, anything -- where stacks were allowed for 'storage'. It's such a pain finding somewhere to put your troops when you're not at war: cities and choke points make sense from a strategic point of view, but leads to traffic jams, but even if you can find an "out of the way" spot it means longer marches when the fighting begins.
Of course most of units should have massive collateral damage to prevent stacking during wartime.