AcDc & GoT have got to be the 2 major versions with differences - they've got 2 additional flippers and a playfield which SIGNIFICANTLY change both rules and scoring strategies.

TWD would come next with the addition of the action button, as well as the crossbow mech.

GB with both the layout differences and the magna slings.

AS has the upper playfield

SW has the hyperloop which can bring in an additional MB, along with the mini deathstar ramp.

Xmen has the moving ramp and pop-ups

Star Trek, Kiss, Transformers & Met have different toys/playfield/shot layouts, but don't significantly change the scoring strategies in the game as a whole.

GotG has an additional couple of magnets and spinners

AV has a powerball which slightly changes rules

Tron has drop targets and an additional MB available

LotR, SM, BM66, Mustang, RS & Elvis are cosmetic differences only IIRC

Don't know enough about TAV, WWE or IrMd