I bought With Fire and Sword after playing Warband because I enjoyed the latter. I found quickly that the SP Campaign in WFaS is lackluster and disinteresting, I heartily recommend ignoring it and buying WFaS for the online gameplay - the multiplayer experience and online community is where it really shines. The game features all the same game-types as Warband (Siege, DM, TDM, Battle, Duel) except with the addition of firearms. If you like M&B but don't like ranged combat THIS GAME IS NOT FOR YOU. Firearms have made shields and light armor relatively useless. Bows are not as dynamic or accurate as in Warband, and the archer class has largely been replaced with the Musketeer class. The fortresses and castle have changes shape to suit the new style of warfare with choke points and high walls with crenelations for the shooters. It can get a little like a shooting gallery at times, but it doesn't feel unbalanced. The Musketeer class gets a bonus to reload speed and accuracy at the expense of health. The Infantry class gets access to heavy hitting melee weapons, improved melee damage, extra health and quick movement to try and combat the range. Players must choose whether to weigh themselves down with heavy armor (to endure a little gunfire) or use their unarmored speed as an advantage in this class. The cavalry class is a marriage of the two maneuverability at the expense of groundspeed and health, this class gets access to carbines, pistols, lances and sabres. They value the open terrain where they can make best use of their speed, and can usually choose to outfit themselves with heavy armour or not to offset the danger of becoming unhorsed. A word on the multiplayer servers: I recommend playing on Westres_Siege or the other Bnet servers for best experience - there's a host of quality custom maps and people. Battle_of_the_Bastards is a good server for battle mode. Best to avoid Sparta-siege though - it's a cesspool of crappy maps, rampant teamkillers and uncaring mods.
It's not the best game around.
