The 360 is only doomed in the sense all consumer electronics are - of course it will peak and fade away, and unless MS are very lucky of course, launching earlier, it will probably peak and begin to fade before the PS3 and Wii.
But, on it's own terms it's been a success I'd say. It's still going strong, it's given MS a good position in US and Europe, and it's sold more than a lot of other consoles have.
It's unlikely I think to match PS1, PS2 and Wii (I just don't think Natal will give it the boost it would need) but compared to Xbox and where MS started I'd say it's been a pretty successful console all things considered.
So no. It's not doomed in the way I think you imply - it's been a success and will fade away politely as a good console to be replaced at some point but a new Xbox.
Try to be reasonable... its easier than you think...
