"highlighting the option to search for applications simply by starting to type its name"; This function was also provided by the start menu.
They replaced the start menu which did not hinder your multitasking with a start screen that blocks your entire screen preventing you from multitasking. Any one that argues you can't multitask because your eyes can only focus on one thing, needs to step away from the computer and go play with some wooden blocks.
I'm not necessarily for or against Metro (I guess I lean more toward the former because I don't use the Start menu and I think Metro is a valid implementation for touch devices), but saying it hinders multitasking hasn't been my experience.
The Start menu provides a pretty one-dimensional, partially redundant functionality. You can open it and search for programs by typing or access one of the immediate shortcuts that are likely on your taskbar anyway -- at least that's the case for me.
Metro requires the same amount of actions to access and search for programs, so that functionality is unchanged. However, you can configure the Metro screen to host live tiles that are relevant to you. Not only does this provide one-click access to a screen of information you care about (at least in theory), it can quickly supply this information in passing. What I mean is, you open Metro to access your email or search for a program and you're instantly updated on a dozen other things without doing anything extra.
That doesn't sound like it's hindering multitasking. What's more, if you're truly concerned about productivity, you likely have multiple displays that will remain visible while Metro is open. All of my communication-oriented applications are on a secondary display (Steam, Pidgin, Post Box etc.) so it's not like Metro prevents me from seeing a new message. I don't think this would be the case even with a single display, because you're only accessing Metro very briefly on a desktop, not using it as your primary interface.