Lol, just listening to the soundtrack for F-Zero GX was enough cause for me to get the game...
There are tons of unlockables and the graphics are also pretty sweet. But as stated before... for me, it was all about the music. Download the soundtrack at Galbadia Hotel; I recommend Infinite Blue and For the Glory.
Oh, and the victory movies are hilarious. You can see some of them on Youtube. Captain Falcon's is priceless, Blood Falcon's is also pretty humorous, and Dr. Stewart's is just... disturbing...
The Story Mode appears enjoyable... the cutscenes are pretty dramatic, (although the Intro to Chapter 6 was kinda corny.) the races that accompany are interesting and unique in their own right- such as Red Canyon in Chapter 2 or Countdown to Death in Chapter 6- and Captain Falcon.... wow, what a hero... whether you respect the Captain or not, the game will have you admiring the guy or respecting him even more.
The bad news? It's gotten nearly impossible to find an unused F-Zero GX game on the market. I'm already on my second copy because the first pre-used one I owned froze up frequently and I could only play Practice Mode for 2-10 minutes at the time... it was too glitched for me to start a Grand Prix or get past Chapter 1 on Story Mode... and what a shame too... I had collected 21 out of 25 capsules when it froze! >.< My second one's been better- I can get through at least two rounds on Grand Prix... before it freezes. I plan to get a disk-corrector kit to see if it'll help.
And most of all- PRACTICE!! Being bad at racing games myself, I was hesitant to purchase the game. But my love for the soundtrack, the admiration I held for Falcon as one of my SSBM mains, and the support I show for Samurai Goroh to earn a spot in Brawl persuaded me. After some practice with each of the cars, I've figured out what works best for me... I aim for cars that focus on turning rather than speed, because turning has always been my weak point. So I go for cars that have a better Grip rating than Boost, with no personal opinion on Body (each one has a rating between A-E, A being the best). My two favorite cars are the Fire Stingray and- you guessed it!- the Blue Falcon.
All in all, YES, purchase F-Zero GX! However, it'd probably be wise to search Ebay for a game in better condition.