Well, I like the round-by-round structure, I like the feeling of "regrouping" and resuming the attack. It would be nice if the between-rounds information was delivered in something more than a screen of text, in the final game - say, a game-engine view of soldiers rearming, administering first aid, etc. I'd also like to see my army total at the top, as well as troop subtotals, so I can understand at a glance the number of losses from the last round.
Also, with one of my characters, I play hit-and-run tactics against tough enemy forces - so the ability to break off and resume combat as I see fit is both well-suited to this style of play, and realistic for an agile and cunning character.
The alternative to rounds doesn't sound good to me - you'd either have to have all the combatants present at once (which is obviously not an option for anyone but top-end PC owners) or drip-feed all of them, as reinforcements, into a single, unbroken battle. That could be tiresome for large forces, and I think it would necessitate a rethink of how ammo is handled in M&B.
But I do like the idea of enemies attempting to retreat from battle - on various different scales. I mean, even within the battlefield - does the enemy AI ever attempt to run away? I've never seen it. It would be cool if a terrified enemy started to make for the edge of the battle map - and if they managed to escape, to then attempt to break from the combat entirely and flee on the world map. We already see them doing this, but only before they're engaged in combat. Here's an interesting idea - doesn't a group with fewer units move more quickly? So, if you chase a fleeing group on the world map, and catch them, and then they were able to retreat and flee again - after you'd eliminated 75% of their number - wouldn't it be possible that they could then outrun you?
Which brings me onto another, minor thing I would like to see (not really important, but it'd be nice). If you're chasing a faster enemy, you can ditch your prisoners and maybe even some of your own men to gain a bit of speed. I'd also like to see the ability to ditch cargo for the same reason. As far as I can see, there's no option to simply 'drop' items from inventory. I could be wrong about that.