As some have mentioned, depends on training and the weapon being used. Pike formations, to be effective, had to be disciplined, and had to stay 'in formation' - look what happened to the scots at Flodden when they lost this. Shield walls also required to keep to a formation - but they were also pretty defensive - i imagine they worked more through attrition. Using an non-polearm requires you to move around freely, (or polearms where unit cohesion isn't the be-all and end-all) which means melees with these weapons would be bound to be chaotic after the first engagement. Also, after a charge, it would be impossible to retain unit cohesion after contact, through momentum alone.

I like the chaos of MTWII battles - especially when you have 20 units scattered all around the place, some routing, some reforming, some not knowing what they're supposed to be doing - its the best bit! (eg: can you get that light cavalry unit back in time from pursuing a broken unit to save your outnumbered general from getting killed?)