My four year old can already score 10,000,000+ on Fish Tales. He also really likes Medieval Madness and Cirqus Voltaire on iOS.
In my experience, he seems to prefer games with bash toys where it's clear what the objective is. So, although he likes our Fish Tales, he can score quite well in iOS Medieval Madness because he understands that he needs to hit the castle, take down the drawbridge, lift the gate and then the castle blows up. Likewise, he enjoys hitting the Ringmaster in Cirqus Voltaire. It takes more convincing him to play games with ramps, or less clearly defined objectives, because he doesn't really understand how scoring works.
Our 18 month old desperately wants to play Fish Tales too, but his arms are too short to reach the flippers and we don't have a tall enough stool. He does keep on pressing the 'launch' button when there's a ball there, though, and he likes pressing the flippers.