Had them both. GB is more fun overall game if setup right. Put Dr. Dude flippers on GB and outlane plastics and the game shines. MET is good and has its adrenaline moments but GB is better sounding, better playing when setup right, and a better overall theme. MET music i never felt matched pinball action and really only liked For Whom the Bell told.
Side note on kids with both titles. i have 6 and 2 yr old boys and the 6 yr old hated MET and loved GB and my 2 yr old loved Sparky and would walk around with a battery and act like he was getting shocked like Sparky. Have a Spider man here now and they both dislike it.