For all its unchanged-ness, the game isn't without problems. The original console game had a dark look and gave players a wide view of the environment, which on the PSP translates to small characters that can be hard to see even with the brightness cranked all the way up. It's not much of an issue when you're exploring, but when you get into a fight, it can be hard to tell whether the guy you're beating on is actually an enemy or just one of your own gang sidekicks who happened to wander too close.
To be fair, the game has zero trouble displaying a dozen or so guys fighting onscreen at once, which - given the level of detail - is no mean feat for the PSP. The handheld's infamous load times aren't much of a problem, either, with missions usually taking between 15 and 30 seconds to load up. The performance stays solid even during two-player co-op, although we did notice a slight lag between the connected PSPs.
There isn't really much to add beyond that, except that we've got high expectations for The Warriors. It's the same game we loved in 2005, only portable and for $20, and we can think of a few other game makers who could stand to learn from that approach.