Pirate's Treasure ($1.99) brings a great measure of cohesiveness to the shooter/adventure iPhone game genre that, combined with a solid upgrade system and decent gameplay, makes for a quite an enjoyable gaming experience.

In suggesting that there is a great amount of structure found in Pirate's Treasure, I don't mean to incorrectly suggest other iPhone games just throw players all over a world with no regard to order, just that Pirate's Treasure is exceptional in this regard.

While a game-like side-scrolling adventure title, such as The Horrible Viking, which I like a lot, provides an overworld map for players to map out their quests, Pirate's Treasure goes one step further by going a few steps back and offering an overworld that suggests something out of a simpler Mario 64. In the Nintendo 64 classic, players accessed levels by jumping through paintings, but only had access to those paintings based on the amount of stars they had collected from earlier, pre-unlocked levels.

In Pirate's Treasure, you're given access to one unlocked level and earn keys to unlock levels deeper in the game. Each level, much like Mario 64, has several challenges in which you can compete to earn more keys. This provides users with a stepping-stone for the difficulty of the game and challenges. You can go at your own pace precisely because the game meters out its difficulty carefully.

Pirate's Treasure also includes some minor RPG-elements in the form of player upgrades. Players can upgrade a variety of categories to make their character stronger, faster and more competent in battle, providing an incentive for a player to play deeper into the game.

The incentive is a plus, but is not necessary to have an enjoyable experience with Pirate's Treasure. As an iPhone game, it plays fairly well. There are two virtual buttons on the screen; one moves your character, while the other attacks as you try to complete challenges like "survive for 60 seconds" or 'collect 10 gold pieces'.

Though, if one sometimes-frustrated reviewer can offer a tip: do not tap the attack button like you're firing off a gun. Enemies will come at you from all angles in Pirate's Treasure; moving the fire button around in a 360 degree rotation, as the game actually allows, provides amazingly better control than the tap-and-fire option.

Visually, Pirate's Treasure is neither the best, nor worst, adventure iPhone game, but it's certainly more than serviceable and doesn't seem to suffer from slowdown, even when the screen is buzzing with enemies.

While your enjoyment of this app may depend a bit on how well you know the source material - pirates only go so far for some folks - this is a well-made game that borrows the right elements from action, RPG, and shooting games alike.