Some of my most beloved iOS games are the ones that perfectly fill those little gaps of time while I'm standing in line or waiting for a bus. Bitsize Games' Robo Surf [$0.99] is ideal for that role, with simple one-touch controls and gameplay that fills a few seconds or a few minutes depending on what you need.

At first glance, it looks pretty standard. You control a surfing robot (what else?) traversing a dangerous seascape. You build waves by tapping, pressing and releasing the screen to control your altitude. You keep going until you hit something or crash into the ocean, and then it's game over. There's a slight twist�you collect oil barrels scattered across the sky to build up turbo, which you can use to ignite your robot and fly straight through obstacles and the bosses that pop up every 500 meters�but the game is functionally pretty similar to endless runners and other obstacle dodgers. So why can't I put it down?

Probably because Robo Surf gives me reasons to keep going. I often struggle with high-score plateaus, but that's not a problem here. You unlock a new checkpoint after each boss encounter, and you can start your game from any of them. If the game were just a high-score fest, this would be pretty pointless�the leaderboards record your total travel distance, not your stopping point�but there's a lot more to Robo Surf than your top score.

The achievement system, for example, is my favorite thing about the game. Some developers include Game Center achievements like they're something to mark off a checklist. There often isn't much thought put into the sort of value they'll add. Robo Surf brings them to the forefront. Every so often, you'll be presented with a challenge: surf for 500 meters, maybe, or collect 20 oil barrels in a row. They're the same achievements you could earn at any point, but it feels a lot more satisfying to meet them this way.

Earn enough achievements, and you'll unlock new characters to ride the waves with. The friendly box-headed Robo, your starting bot, can be replaced with characters from three indie PC titles, Walkie Tonky, Iji and Blueberry Garden. The upgrades are purely cosmetic, but having them there as a carrot kept me playing to earn achievements, which in turn encouraged me toward more creative and challenging ways to play. By the time I unlocked all the playable characters, I was utterly hooked.

It helps that Robo Surf looks and sounds great, with engaging art and a cheery retro soundtrack underlying the action. There are lots of goodies to look at, between the cartoony birds, bats and bosses, and the backgrounds that change every few hundred meters. And if you need more to do, you can give the speedy 10 Wave mode a shot. This gives you ten touches to try to earn the best possible score, a short-form challenge that's inspiring some fierce leaderboard competition.

Robo Surf is lighthearted and fun, with enough hooks to turn it from a momentary distraction to one of my new favorites. Our forum users are loving it, too. It's hard for a game to stand out in such a crowded genre, but this one shines. Be sure to give it a look.