ACDC is broad, in that it has 12 modes, but you can choose any of them at start... you can see most of the game just by replaying. All three multiballs can also be started pretty easily... only Encore mode is tough to get. The rules are very complex and scoring well takes skill and knowledge, but the game is mostly visible to anyone
TSPP is deep in that many of its modes (and mode stacks) cannot be achieved until many other goals are completed. Only very skilled players will experience things like Couch, Pretzel, Springfield Mystery Spot and Scratchy's Revenge stacked together.
LOTR is not as deep as TSPP in that it doesn't hold as much back, but things such as SRFMB, TABA, and of course Valinor are there for the long haul. LOTR is broad in that it offers many scoring opportunities at any given time... ring modes, movie MBs, ring frenzies, Gollum MB, 'super' awards, etc.
Xmen seems pretty basic in that you can have a villian and a hero running, or not, but the intricate details on how those villians and heros interact with the multiballs makes the game complex. No comment on hero stacking, that just gets silly.