Other M isn't rock bottom. A whole series of Other M's to the point that that is the "normal" design for a Metroid game is rock bottom. It's like how with Sonic the problem wasn't that Sonic Heroes was a bad game, it was that all Sonic games after that were crap. It wasn't just a mistep or one bad title but a whole series of them to the point that the whole brand is associated with crap. I would rather tell kids of future "did you know about this series called Metroid?" then to tell them "did you know that Metroid used to be GOOD?"
I'd go so far to say that Sonic Adventure (maybe 2) established a fundamentally broken architecture that Sega never managed to veer away from. I gave Colors a shot based on its positive reception, but it didn't feel significantly different than previous efforts to me, other than being streamlined. People concentrated so much criticism on the mech/combat/werehog levels, that I think the "fast" stages got a pass, when they're really only good comparatively.
By way of that, I think Other M gave us a pretty decent glimpse of what a 3rd person Metroid is going to feel like in the hands of most developers, and it's best to stay far away from that until someone can totally rethink it from the ground up. Right now the options are classic 2D style (verified great!) which I don't see Nintendo doing with the 3DS or the First Person Adventure style (verified great!), but I really doubt anyone would want to follow Retro with that, and Retro clearly has had its fill (which is fine).
I'm kind of leaning toward putting Metroid away for another decade chill. I don't think we're going to top Super Metroid/Zero Mission on the 2D front, and I don't think we're going to top Metroid Prime1/3 on the FPA front. And 3rd person is tainted, if not simply unworkable (in the sense of AAA success).