I think the skill shot on Metallica is amazing. It actually requires skill to get the big reward. I think Bowen discussed this one in his tutorial?? I certainly didn't figure it out on my own!
If you hold the left flipper while plunging, a skill shot is awarded by hitting any of the major shots. However, if you hit the shot that is flashing (randomly assigned after plunge), you lock in the inserts and get a playfield bonus.
It's very hard to accomplish. It takes all of your attention, and pulling it off is very satisfying.