Pepsi is going through an identity crisis. Or at least it feels that way with their announced rebranding of their full line of drink products, which includes a redesign of the iconic Pepsi logo.
I get what they're trying to do: pull back and simplify. Much along the same lines of what Coke did last year. The problem is, it's not working for them.
The reason it worked for Coke is because they pulled back and eliminated superfluous elements and kept the logo very simple. I think Pepsi is diluting their brand equity. Had they simply refined / simplified their existing logo instead of screwing with it and changing it they would have a better chance.
The thin font for Pepsi and Diet Pepsi feels disconnected with a semi-successful attempt at a throw-back by modifying the "e" to look like the soon-to-be old logo. If the mark and the logotype were more tightly integrated they'd be on to something. Sadly, the Pepsi and Diet Pepsi cans are the most "successful" of the butt, uh, bunch.
Sierra Mist is too literal and looks like something a first- or second-year design student would do. Or as one commenter contributed, it's something an intern would do. And the Mountain Dew logo looks amateurish at best. In the end it'll probably work out. It won't make it good. But it'll be there.