I have a better idea. You just go and download Super Metroid right now.
Although... if you really want to hear why Metroid Prime 3 is way worse than the first two games:
It doesn't have one big overworld, just some lame small ones, you don't have to backtrack at all, because your ship can just take you everywhere, there's too much shooting, too little puzzling, the music sucks most of the time, the Valhalla level is too scary if you play it while it's getting dark(there's still some daylight when you start, but when you save the game and quit everything is dark and you didn't even notice), human NPC models look kind of scary, there's quite a lot of illogical one-time scans(like the Aurora Unit in Sky Town- keep your eyes on that one), the game is way more fragmented, so you don't just travel through an area to be surprised with a boss, but you just go to a leviathan to beat one, for example, the controls aren't THAT much better than the controls of the first two games imo, the Metroid Dread-reference doesn't mean anything, it's just a mean joke, the graphics in the cut-scenes are so pointy that a fakir from India would cry out for mommy from just seeing it(this is on a HDTV only).
That about sums up everything. Most things that are bad about it are because the game had two really great prequels, you should definately try those out some time.
Sleep at night with this in mind: I'm waiting for a game that's not nearly as good as its predecessors.
You'll be surprised how damn good it is when you play it.