If you are talking about the introductory box set... its almost impossible to find the older versions. I'm not even sure the 25th Anniversary one is still in production. I'm not sure exactly which version each of the intro box sets are, so I'm going to assume the 3rd edition was the most recent before the 25h Anniversary, in which case it has pretty much all the same stuff but the Anniversary one has a Thor and Loki test production run of the new high quality plastic line they are talking about developing. It might also have a bit more fluff in it but I'm not sure.
Steampunk Farseer thanks to The Randomizer
Derby, UK and Bleak Despair battlestation. Species: Spirit-Bound Skeletal Lich (Lawful Evil)
Re: Battletech-New or Old?
As I recall, one of the more recent version attmepted to toine down pulse lasers to act more scatter-y like or something, and/or not cumulative with targeting computers (all of which I completely ignored as unecessary - Battletech is fun, but is waay slow at the best of times, it certainly doesn't need slowing more! We never bothered with the torso-twist phase and require mandatory salvo fire in our games; heck, at the last count, I was bolting on the action sequence from Manouver Group with moderate sucess, so you may all freely call me heathen for sulling the purity of the game with house rules...!)
There are a few rules that changed. The most important is that partial cover used to give +3 to the TN, but caused hits on the Punch table (thus, if you do hit, there's an increased chance of head shots). Now it only gives +1, but leg hits do no damage.
We never bothered with the torso-twist phase and require mandatory salvo fire in our games;
I don't believe I have ever played with anybody who explicitly declared torso twists; they just get figured in as a matter of course when you're considering possible fire arcs. Only time it makes any practical difference is if you might want to split-target between two possibilities that are spread far enough apart that twisting toward one will remove the other from your fire arcs..which is a niche enough corner case that I don't think anybody really cares.