Tron is a good pin for comparing to IM and MET. MET is a little better, IM a little worse ... all are close and the best one of those depends on your own preference. Since you already own two, SM offers a much different option. Steve Ritchie design, SM is much more game than BK (which also has great flow but is not as complex as a dmd). Regardless of which game is better, SM is more different from your current collection.
SM is a fantastic game - classic theme, solid build, easy to understand rules, plenty of flowing goodness. The negative factor is long ball times (like LOTR), but nobody would accuse it of being similar to LOTR. If most of your time playing SM was before later code and you still have fond memories of the game, you are going to love the game now. I can see you getting a SM now, and someday later convincing the family to let LOTR go.
The journey is dangerous and often difficult. Those encountered along the way (family) and their expectations must be managed....