I'd be willing to bet that Rengoku: The Tower of Purgatory started out as a technical demo for the PSP and was quickly turned into a retail product when someone at Hudson figured out (quite correctly) that any game going on sale during the PSP's launch window would sell enough copies to at least recoup the development costs. I also have a hunch that that's why Konami picked up the game for a North American release.
I'm not sure what Rengoku means exactly, but "tower of purgatory" is a reference to the game's main location. Players control an android named Gram, who, after killing thousands of human beings for his unknown masters, decides to seek out the reason for his existence by scaling a 10-story tower. The tower is filled with other androids, which Gram has to defeat on his way to the top. As players defeat the boss on each floor, Gram learns more and more about why people fight and what his own motivation in life is.
Gram is highly customizable. It's also very easy to just jump right in and start kicking ass with him. At the start of the game, you can attach single weapons to each of his arms, his head, and to his chest. Support items, such as shields and energy boosters, can be attached to his legs or to any of the other attachment points on his body. Later on in the game, you can use the credits you obtain from selling unwanted weapons to upgrade Gram's stamina and shields, and to add additional attachment points to his arms, head, chest, and legs (allowing you to attach heavier and more powerful weapons). Using these weapons is easy. The square and circle buttons activate the arms, while the triangle and X buttons activate the head- and chest-mounted weapons. The digital pad controls Gram's movements and the L trigger lets you lock-on to enemies.
The combat interface itself is great. Certainly, the ability to control each of Gram's limbs individually puts players that much deeper into the gameplay. The whole concept of an artificial lifeform fighting his way to the meaning of life is interesting too.
Sadly, the overall execution of the game is underdeveloped and, at times, counterintuitive.
First off, the rooms that make up each floor are repetitive and dull. Each floor of the tower is made up of anywhere between ten and twenty nondescript rectangular rooms. The rooms are all painted the same shades of brown and gray. To make matters worse, the only interactive objects inside each room, aside from the androids, are square crates that you can blow up (which contain useful stamina and cool down items).
Secondly, there's nothing at all to the combat. Inside each room is one or two–sometimes as many as three–androids. That's all. Enemy androids aren't very good at dodging your attacks and their weapons are either too weak or too strong compared to Gram's. If they're weak, you simply blow through the floor and move on to the next. If they're too strong, you hightail it downstairs to previous floors and collect items until you can afford the necessary upgrades.
One of the game's lamest aspects, bar none, has to do with how weapons are installed and reloaded. You can only install new weapons and reload ammunition at the computer terminal located at the entrance to each floor. That may sound reasonable, but in practice you have to return all the way back to the entry way five or six times per floor just to keep your ammo levels up. This means you'll spend that much more time going back and forth through all of those aforementioned gray and brown rooms.
There's really nothing else left to say about Rengoku. The graphics are sharp and the animation is smooth, which is what you'd expect from a PSP game. Jun Suemi's android designs are unique, to say the least. It's not often you see a robot with a pistol sticking out of its skull . It's also nice how Gram's different body parts change visibly when you interchange the various weapons and attachments in his constantly-growing inventory. The audio is peppy and techno-centric too. Ultimately though, all of these things are wasted on a game that literally involves clearing out the same room over and over and over again for roughly four or five total hours.
Also, there's an artwork gallery that unlocks as you clear each floor, and an ad hoc wi-fi mode that lets you trade items and fight against nearby friends. Seriously though, how important are these extras if the game itself is so mind-numbingly underdeveloped?