As others have said here they are entirely different, there is no comparison.
Flight of Passage has very little actual motion - it's all cleverly simulated with the use of 3D and tilting hydraulic platforms. It's closer to Soarin than it is to Guardians.
Guardians is a dark ride roller coaster that launches you backwards in the ride car from 0 to almost 60mph in seconds. It spins/spirals around the tracks at 60mph for basically the entire time (around 3 minutes). It's like space mountain in terms of theming (space, dark) but is much more intense. If you like roller coasters then you will probably love it. It has stunning visual effects and an amazing soundtrack (one of 6 random songs). If you get motion sickness or vertigo easily - you might want to bring a barf bag. It is similar to Expedition Everest in terms of intensity/thrill.
That being said - they are both in my top 5 favorite rides at WDW so I hope you will give GotGCW a try and let us know what you think.