If you've played Whirlwind, you'll feel right at home with Earthshaker. Very similar objectives: Shoot the lit targets as indicated by the institute to advance towards multiball. Shots up the main ramp advance the captive ball (which acts in the same manner as the tornado drop target on whirlwind). I will say that Earthshaker does have a really good playfield. I've always thought it was one of Lawlor's better designs. The inner loop shot is repeatable (similar to shadow loops), the lock shot is infinitely satisfying, and feels similar to the open bookcase shot on TAF, and the right ramp jackpot shot feels smooth. The state diverter is brilliant. There are some other interesting nuances: during 3-ball multiball, a shot to the shelter will hold the ball indefinitely until one is lost. Without flipper staging, this code feature makes shooting for jackpots a little more interesting. Quick multiball can be stacked with regular multiball for unlimited millions and a jackpot. It's just a terrifically shooting game.
ES has 2 big downsides: The jackpot can only be collected once per multiball (no way to relight), and to a much lesser extent, the center ramp can be spammed for miles. Once you reach 99 miles, the player is awarded a 200,000 pt "end of the road" bonus, which is really lopsided. Granted, doing so takes a ton of time, and is woodchoppy as all hell. It's not a quick rules exploit like the unlimited millions from Police Force.
If you have a larger collection, ES is a great game. In a small collection, maybe look for something else.