'Wonderful'? I allllllready killed them. When the bad guys keep coming back to life am I supposed to feel nostalgic and happy inside?
It's like winning the Special Zombie Olympics: even if you win, the retards keep coming after you. Eventually I'm not going to want to participate, not even for charity.
The bad guys can be cloned. I take you hate the Mario games then? Villains always come back in them, or Zelda? Nostalgia mixed with fresh elements can be a very good experience. It is like when the Koopa Kids returned in Mario and Luigi, it was a fun moment for fans of the series. It is ridiculous that Kraid never made an appearance in any of the 3D games, while Ridley is in every single one of them.
Here's the key difference, though: Mario, like Zelda for that matter, is a mockery of continuity. Each branch of that franchise is essentially its own independent universe that shares similar things. I am sick to death of certain enemies in the Mario universe (like Bowser and Bowser Jr.), but there's nothing really preventing them from being logical bosses in those games.
The Metroid universe, in the other hand, has had a fairly strong emphasis on continuity: each game takes place in a specified point in the timeline and events from each game generally matter in the game that follows. Given that, it takes a great deal of fun out of the experience knowing that there's no real accomplishment to killing someone like Ridley: he'll just get resurrected for the next game in the line, usually with no explanation for it. There's permanence to everything in the Metroid franchise
except the enemies and it gets kind of tiring after a while in a franchise that's as pseudo-serious as Metroid. If they're not going to even try to pretend that there's meaning behind taking these bosses down, I'd prefer new bosses that can be perma-killed.