After owning TZ for a year, I never could figure out why it's the #1 game either. It has nice enough shots and really cool features (magna flip, powerball, gumball, etc) but when you get down to the meat of the honestly the software for the doors is a little lacking. Almost every timed mode is kind of lame relative to other games if you think about it...
spiral--hit the loop, hit the loop, hit the loop, hit the loop...
super slot--hit the slot, hit the slot, hit the slot, hit the slot
clock millions--hit the clock, hit the clock, hit the clock, hit the clock...
clock chaos--hit the clock, hit the clock, hit the clock, hit the clock...
town square madness--hit anything
There's no sense of progression or anything in these modes (i.e. goal). Just shoot the same shot over and over, awesome, lol. Can't I hit one shot, then a different one, or at least have multiple options? Relative to a game like Indiana Jones, where you have things like hit the shot where the monkey is, 6 ball well of souls, save the stones, etc--every mode tells a story. It just seems like TZ has a lot of cool pieces that don't really integrate that well with each other.
For my money, TSPP is a lot better game from a software standpoint. And it's probably cheaper. I think too many people get caught up with modding the game that they lose sight of why they own it.

For the same (or less) money I think IJ and St:tng are better games as well, if you prefer Williams games. I guess my overall summation is that if you prefer stacking games, TSPP is WAY better, and if you like mode based games, St:tng and IJ are WAY better.