I've never played the original Metroid Prime on the Gamecube - I own it, but for some reason I've never found the time to load it up. However; I've played Metroid Prime 3 on the Wii, but didn't like it, and 2 is even worse. So not expecting much from the original, but I'm aware it's considered the best of the lot.
Resi 4 for me is the best Gamecube game ever... then I'd have to recommend ikaruga and Rogue Squadron 2, I loved the cinematic feel and gritty graphics.
A crying shame this console didn't become more popular, but as someone already mentioned the price of the games then and now are stupidly expensive.