Pinball, like card games, slot machines and casinos, has become almost entirely digital these days. There's little need for the original, physical components - no need for ball bearings, decks of cards or roulette tables. Pocket Gamer's games systems have recreated them superbly well and the extra convenience of a pocket-sized pinball machine is hard to compete with.
But the same rules apply. Virtual tables, like real ones, can be poor of design, with entertainment value that drops between the flippers like a hapless ball bearing. But pinning down exactly what elements make for a good pinball game is considerably more difficult than picking out the faults in, for instance, an iPhone game.