Battalion: Ghosts is the sequel to Battalion: Nemesis (which I accidentally rendered as "Battalion Nemesis").
This game sees improved graphics, more diverse gameplay, and various other improvements, and its storyline builds on the previous one's. It also uses the same gameplay engine as a multiplayer version.
In a sentence? Everything's better.
Which isn't to say that you shouldn't play the first one; you should play that one and then this one.
There's a third game; maybe that'll be the one I finally have time to do a full writeup for.