Never played these games before, looks kinda fun to be honest. :)
Do you fight with your own army in the game or do you fight alone?
You fight alongside an army against an army, but you only control one character in a battle. In story mode, this character is chosen for you (in DW7) but in chronicle mode you can pick one of 63 different characters. You cannot change your charcter mid-battle and you don't direct troops. Generally you just masacure their troops and officers and rack up hundreds (even thousands) of kills. Normal enemies generally just stand there and let you kill them (though some try to fight back. All the worse for them) but officers can be quite a challenge, especially on the higher difficulties. I can't give all the details as I have yet to get DW7, but what I've said applies to most past DW games.
I think it's fun but if you've read any of the earlier pages, you will notice that opinions on this differ. If you're not sure rent this game or see if there's a demo of a previous one available. I think there is a DW gundam one on XBL, but they're very different games. For one thing, that one has robots. I didn't like that one but I think the gameplay might be similar.