IM all day all day.
I just played Met pro extensively last night, to see if I will add it to my collection. Met has awesome art, but overall the game was not my cup of tea. Not sure if always, but it seems like most orbit shots are stopped at the top and dropped into the pop bumpers. Not a fan of that one bit.
I think Met is excellent, but IM (to me) is one of the best games ever. I list it number one in my collection.
Also, theme for me is like A+ IM and like C- Metallica. The music and callouts of Metallica (to me) would be overbearing. Just my 2c. But for me it's a slam dunk decision between these two games.
I know IM is shallow, but that's one think I also prefer. I have several longer games, but to me IM and Tron are just deep enough.
This is just my 2c and I'm sure others will disagree.