I find Metallica to be a real grind. 10 hits on sparky for multiball. ~10 hits to snake mb. like 40 hits for coffin. Collect 15 of each 4 items to light crank it up, do that 4x for the final wizard mode. It's a fun game but it got old for me eventually. Then again I've played it a lot more than I've played SW so far...
Metallica has some cool rules involving the items, completing shots, hurry-ups, and crank it up, but the rest of it is very standard. SW rules are very non-standard. Play modes to light multiballs, the modes can't be timed out, so you have to learn how to play ~14 individual modes to be able to play it well. I find that really fun, and spent weeks on the game just playing each mode and figuring them out. Other people hate it though, they want to just shoot the lit shots and not have to learn all this crap.
Metallica's shots are easier and feel good to hit. SW's are all a bit difficult (narrow, further away). You tend not to hit a shot on the first try, and need to recover and try again, but I don't find myself failing to hit them too much once I actually get control and aim properly. It wants you to go fast, but fast is dangerous, so you've got to learn to balance it.
People who play R2D2 all day don't know what they're doing. I get high scores with every character, and I don't choose R2 in competition either. I think the best points come from Leia, but you have to get to the mini-wizard modes to get those points, so she can also be the lowest scoring. Having the four characters each with their own sets of modes keeps the game refreshing a lot longer than I'd have expected. On most games I figure out one 'path' through the game but on my SW I choose a different character, and then choose which mini-wizard to go for, and my strategy changes completely for all of them.