Generic beat em up, 100% likely it's just a GBC game put inside a GBA case since, well, that's obviously what it is :p The engine also is exactly the same thing used in Metal Gear II.
I forgot to say Metal Max II uses the same music in the first town as you hear on the world map of Final Fantasy IX. Other music like in battles I've heard in other Sintax titles, can't remember which. There's also another Sintax title i got some time back called 海戰奇兵 which appears to be a hack of that Fire Emblem game from SKOB or whoever. Same music and setup and everything.
As always after buying Sintax stuff, I ask myself why do I keep buying this stuff since it's always crap lol. None of the really interesting titles ever pop up, like Zook Hero 3.