The problem with my historical gaming is that I sell off projects and then get back into them later. I've done this with samurai, British colonials, and the Franco-Prussian War. My first 15mm FPW project was They Died For Glory. I spent 14 months painting up a 15mm 1870 French Division, and 15mm 1870 German Corps. In the end, I used the battle of Weissenburg as the basis of my generic 15mm FPW game.
Now, I am back at the grinding wheel painting up 28mm FPW armies. What have I learned from all this?
Don't get me wrong. They Died for Glory is an excellent rule system. It is playable in both 15mm and 28mm. One of the problems with They Died for Glory is the scale of figures needed for corps or army level games. Some of the scenarios say they can be watered down if players don't have enough units. I just could never paint up two corps of French troops. It is enough paint up a corps of French or Prussian infantry. The basic unit is an infantry battalion or cavalry regiment. A division might have 12 battalions. That is a lot of figures. I sometimes think it might have been better to have used the Wargames Illustrated issue back in the 1990's about a Fire and Fury variant for the Franco-Prussian War. You could play the game at a larger level of organization. There's also Volley and Bayonet.
They Died for Glory came across as more tactical rule set designed for big battles. The game mirrored the historical battles where divisional skirmish lines protected advancing columns of German infantry as Prussian Krupp batteries shelled their French opponents. Nothing sexy about that. Just a pretty vulgar fight between the masses. Lines of skirmishers became key for any possible German attack on a French position. If you could wipe out the skirmishers, then you could stall out the German attack.
I've now moved my figure scale up to 28mm. And my organizational level is now at brigade/divisional. I'm looking at completely my first 28mm 1870 French infantry brigade this month. I've also am basing a 28mm 1870 Prussian infantry brigade this week, too. Chassepot & Needlegun doesn't make use of skirmishers. That is the biggest difference between it and They Died for Glory. You can play a brigade sized game with Chassepot and Needlegun. You can't with They Died For Glory.