Simply one of the best fighting game ever made.
Okay sure, The AI is predictable, the gameplay lacks a ton of modern fighting gimmicks, the music is nice but a bit too generic, and the graphics while smoothy animated are not really all that impressive especially by modern standards,
So why is it one of the best fighting game ever? Just one thing:
For one thing, instead of simply having stock characters with fixed stats and moves, you can choose a combination of pilots (for different stats) and robots (for different move sets). In addition to this, "Tournament Mode" allows you to build your own pilot and upgrade your robot further allowing customization. There are also a few secret moves and upgrades that can be obtained. The only fighting game that offers more gameplay-related character customization options is possibly the Dragon Ball Z: Budokai Tenkaichi series (which is not that bad but a bit eh).
Aside from character customization, the game also offers tons of gameplay settings that can be tweaked (most involving secret menus), including enabling "Hyper Mode" which adds new features that almost completely changes the gameplay balance. The only fighting came that might compare is the Super Smash Bros. series (and I should add One Must Fall, like SSB, also features stage gimmicks which can damage fighters, but the stages are much much smaller... well relative to the fighters anyway).
Also the story is okay too, but who cares about story in a fighting game?