see IMO voice acting should never even come up in a metroid conversation at all, unless its whether samus should have an internal monologue. the whole reason the atmosphere works so well in metroid games is because of isolation; it is just you and your precious armor versus an entire planet of completely alien beings and a very hostile environment. Your powerups and upgrades gain significance beyond just allowing you to explore this alien place more actively; that armor is the only thing standing between you and a whole planet of malice!
You can tell other metroid stories, sure, but they will not work as well, or be evocative of the emotions or feelings that people have come to love about the series so much. As soon as live humans (voice acting or not) enter the picture, you lose that, and to me that is a very big loss. Metroid Prime's atmosphere is way better than Echoes', largely because Echoes starts out with you surrounded by space police, and watching a cutscene of space police being attacked. The attitude is all wrong, and it gives you too much to connect to. Samus is supposed to be your one human anchor in the world, the only thing you can identify with; and by doing so you better inhabit her character - alone, The Hunter, contained in the suit (Prime's visor sells this idea sooo well!), and navigating a hostile world doing its best to snuff you out. The constant and bizarre flora and fauna of Prime helps to accomplish this so well, versus the weird static webbing and crystal structures of Echoes.
To me, if you're not telling a story, or better letting people play a story, about an isolated warrior in a completely alien world, then you're not telling a metroid story, and you should probably call it something else, regardless of whether or not it has morph ball puzzles (the highlight of Echoes, far and away).
