Matter of opinion.
Hmm, Metroid could be better but I found this more fun. It's like some movies are really good but I'd rather watch Happy Gilmore ten times in a row than watch 12 Angry Men twice in the same decade.
I played all the Metroid games (minus Prime 2) but lost interest in all of them before finishing...well except for Metroid Fusion but it had so little replay value after I beat it that I sold it away. Four hours compared to DoS which is nearing 30 hours on the second mode.