The Immortal Solid is one of my all time favorites. The ball was fairly early, strong yet smooth. I really like how it rolled through the pins. I dropped from 16 to 15 a few years back, thus it moved out of my bag. I was recently looking for a 15 that I could use as my oiler. The ball has an unusual drill technique so you will want to make sure you have the drill instructions (or search online).
All in all, I would tell you that if you can get a hold of one, it is well work the investment.