Ian,
I have just scored Nova Games Battle for the Factories, I had it and Fire on the Volga during the mid to late 80's, I prefer Nova's counter art and colours, how does SoS play as opposed to FotV & BftF?
Can't really answer this Perry, I briefly bought both BftF and FotV, front covers on the box look great. I was disappointed with the look/size of counters and map within BftF/FotV compared to SoS. To be fair BftF/FotV as you mention were both produced in the 80's and this was standard artwork for the time. SoS for me with the bigger hexes and more colorful counters is more polished. As for the rules, i dont know if there are any big changes - i think the artillery bombardment rules may be different.
A lot of people are put off with the amount of phases within the sequence of play, with artillery having 4 seperate bombardment phases, being able to fire in support of attacks and interdiction within movement phase. The key thing though is that artillery can only fire 'once' and its upto you as the player to decide when do you fire. The actual mechanics of the game are quite simple and playable for a monster! and it really gives you a 'good feel' for the issues both sides had i.e as the russian player you are desperate to get more troops across from the east bank of the volga to fill the holes from the german onslaught, as a german you constantly feed in troops to get a 'breakthrough' into the city, however route of advance for your armor is limited by the balka's.
If you go onto Boardgame geek - download V2.1 of the rules to have a quick look at the changes between the two versions.
I believe a 4th edition could be in the pipeworks - will definitely have to have a copy of this
Regards