Space Harrier... seriously? It's like Dragonball Z on hallucinogens meets Lucy in the Sky With Diamonds meets the Star Wars arcade game. Truly a bizarre third person rail shooter. I couldn't tell you if it is fun or not, my brain is still soaking in the oddness of the visuals and I'm scratching my head.
You are kinda jumping and flying through the levels and shooting enemies with the cannon under your arm. It all kind of blurs together, but if you squint and imagine you are an X-Wing fighter in the trench on the Star Wars arcade game you can sorta get into it better. But I don't remember Darth Vader saying "Welcome to the fantasy zone!" What the heck is that all about anyway?
So my best recommendation is to actually play this game and form your own opinion since I'm a little too confused to form my own.
I would say that the game play for this cartridge rates 5-10, controls 6-10, and overall 5-10. In the land of Bizzaro I'm sure this is a great game, but I'll leave that to you to decide.