I've tried forever to like Metallica. I first played the pro when it came out, later I played it when I was deciding to get it or IMVE. Later I played the premium thinking I'd like that better. Just the other day I played Met pro again, after all so many people say it's the best. But never did I think it was all that great. I love the art package and the metal ramps and the grave markers. I don't love the way the ball is stopped at the pops on loops so often, I don't love Sparky as much as other people. I do not really care for the songs in Metallica they are too droning whereas ACDC songs are up beat and kicking ass. I don't like the call outs on Met at all. Overall to me it's clearly the least fun on you list (just my opinion) but by far it's Tron/AcDc premium (and I can't decide between those and IM so that's my top 3).
On Met, I don't think there is a signature shot like Gem on Tron or Bell shot on AcDc or center shot on IM.
I think Tron is better overall than AcDc for me because I live the theme, immersion via the call outs and music and sound effect it's my favorite pin. There's not a thing I don't like on Tron. I love the short, simple rules and SOS, some people say it's too easy but to me it's just right as I'm not the greatest player. Love the third flipper with the Gem shot as well as the side ramp. Love the Quarra shot to feed the upper flipper. Overall just about a 10 in every way.
To me AcDc is more fun sometimes than Tron because of the atmosphere where you got the great lights like a concert and the great songs and the call outs by SR are fantastic and great pressure shots for big points. AcDc has more rules than Tron, they are quite complex, I still am learning some of the nuances. I like how each song gives a different mission and makes the game play different and you can get song high score. I like the lower PF on AcDc but wish it was more integral or coded somewhat more. It's fine but could be better. I like the cannon on AcDc but sorry it blocks so much of the inlane and out lane.
I'm going to add IM here because it's also short rules shorter than Tron but it's a blast, great theme great call outs great intensity. Overall it's lightning in a bottle. Kind of a mix of intensity of AcDc and fits together 100% like Tron without a bad shot to be found.
Tron and IM I love to death, I don't need to have a good score or a long game to love playing it. I can have three balls in under 2 minutes and it's still fun. A game like SM or XM or Potc if I don't make strong progress on a game it's not as fun. I think Tron and IM being so short it lets you see a lot of what there is in a shorter time.