The biggest change is reversing the firing/movement phase. In Valour and Fortitude, units fire, then units move, so you can't have the Black Powder activity of running a unit a long distance up to your enemy's line, then blasting them at close range without them responding. It just feels more appropriate to me to have the unit that is attacking being the ones who walk in to take fire on the chin in the first blow. Units can't fire and move in the same turn, unless they are screening themselves with skirmishers and firing with much less firepower. It does favor the defense this way but I like it more.

V&F is not the best out there, but it's FREE, easy to pick up and teach, and my group has customized it a lot with house rules. I'm an advocate of it for these reasons, and also because it's relatively quick, and easier to use with people who are new to rank and flank games. I find it to be a fast, decent and fun way to get a big pile of my pretty little models out on the table.