TNA is my favorite pinball machine, hands down. I have a smaller collection of games (BK2K, R&B, RFM/SWEP1 and a couple others) and have never had the enjoyment with them as I do with TNA. I think it has something to do with the complete package (gameplay, art, lights, sound, etc) coupled with intentionally
shorter game/ball times, bit-sized sense of accomplishments (setting up and hitting multi-ball, blowing up a reactor -- even if it is reactor 1, hitting the skill shot, etc.), an easy to understand yet difficult to master rule set, and a game that is forcing me to learn pinball techniques (nudging, passing, catching, etc.).
As many have said in this thread, it has that "just one more game" feel to it which none of my other games really do.
I got into the hobby ~5 years ago and I'm not a good player by any means so take what I say with a grain of salt... it also doesn't hurt that my 8yr old daughter is my partner in crime with pinball and I pretty much have at least a 2 player game whenever I want