Doodle Jump is one of the reasons I even bother with iPhone games to begin with. Instead of trying to pack a complex console idea into a shoddy iPhone format, Lima Sky's latest iPhone effort is simple in scope. And at a 99-cent price tag, with quick gameplay that breeds addiction, what more could iPhone gamers ask for?

Doodle Jump starts with an art style that aptly looks like something one might have doodled during an algebra class. The background is always graph paper, after all. The main character is some sort of small alien, with green skin, a long snout with projectile power and tentacles underneath that cause it to bounce.

Players hold the iPhone vertically, and find a vertical path of bars of various colors. Green ones are static. Blue move left and right, while grey move up and down. Yellow bars will eventually turn red and explode, while brown ones are made of wood that's ready to break apart.

The alien just keeps jumping, at the same pace, with the same amount of bounce. It is up to players to tilt the device left and right to help the alien continue on its journey upward. The bars appear in randomized fashion, so players must stay on their toes to navigate the winding path, because one false move and it's over. Once any bars disappear off the bottom of the screen as the player moves upward, they are gone for good. So if the player makes a mistake and plummets, there's nothing below to stop the alien from falling, falling, falling.

The alien has the ability to transfer off one side of the screen and reappear on the other (a la Joust). Players can also boost farther up the screen with the aid of items strewn about the bars, such as springs, trampolines, propeller hats and even rocket packs. As the goal is to see how high up the board one can get, with the high score being based on this elevation, any boost to make progress faster and skip obstacles is a helpful one.

But two main things work to keep the player from reaching new heights. The first is the simple structure of scrolling up the board. Sometimes it might seem like a good strategy to drop down to a lower platform for an item, or to realign on a new path, but what often happens if players aren't careful is that they will ascend too high on the bounce, and that lower platform is no longer there, spelling doom for the player who already committed to dropping back down.

The other obstacle is more doodle-drawn monsters that appear to hamper progress. They move around on-screen, blocking paths. If the alien touches one without a shield, it's game over. So players have two options - either try to navigate around them, or blast them with projectiles. The latter might seem a better choice, clearing the path first, but one must remember that every tilt of the device changes direction and the villains pop up with speed. Navigating and directional shooting at the same time can get complicated. So while the gamer is focusing on placing a nice shot, he may also be sending the alien off course to its doom. Holes punched in the paper also act as traps through which the alien can fall.

There's nothing else to the game, other than an alternate mode that gives everything a wintery theme. In this mode, the alien dons a Santa Claus hat, the background is filled with snowflakes, all of the bars are snow-covered and white, and even the bad guys come with some holiday flavor. Interestingly, the change in theme actually makes things ever-so-slightly more difficult, as players can't rely on the colors to know what lies ahead, but must keep an eye on the movement of the bars. The projectiles are also snowballs in this mode.

The charm is a large part of Doodle Jump's success, as it has the feeling of someone's notebook doodles coming to life in a fun game. The fact that the fun game controls well and uses simplicity to its advantage seals the deal. There's a reason that Doodle Jump is sold on iTunes with the sub-heading, "Be Warned - Insanely Addictive" - the game is just that. Its straightforward gameplay and constant challenge with lack of a true "end" means Doodle Jump is the kind of title that will have players repeatedly saying, "Just one more game." So be warned - just like drawing in a notebook during class, Doodle Jump is an activity easy to get lost in.