This is the Google visual brand / brand. It is simple, childlike and friendly as they want their brand to be perceived. Is this a good perception? They think so and they have given us detailed info on their reasoning!
google logo 2015

1  It’s The Future
What the say in Google’s official blog.

“We think we’ve taken the best of Google (simple, uncluttered, colorful, friendly), and recast it not just for the Google of today, but for the Google of the future.”
“…our goal of making Google more accessible and useful to users around the world, including the next billion.”

2  It’s Simple

The new Google logo was designed collaboratively by internal teams. The rationale behind the changes?
What they say:

“The Google logo has always had a simple, friendly, and approachable style. We wanted to retain these qualities by combining the mathematical purity of geometric forms with the childlike simplicity of schoolbook letter printing…”

google type

3  It’s Type and Design Reasoning
Their principal justification for the redesign? Optimal readability and legibility.
Product Sans, their geometric sans-serif typeface, complements the logo. Optimal readability was a central focus as it is often used in very small sizes and at low bandwidths. Clarity on everything from a 2.5-inch watch face to a 50-inch TV! When type is scaled, a strong typeface can carry the message well at all sizes. The new “g” is simpler and conforms to the new geometric structure based on circles.
What they say:

“The old logo, with its intricate serifs and larger file size, required that we serve a text-based approximation of the logo for low bandwidth connections. The new logo’s reduced file size avoids this workaround….”
“Our new logotype maintains the multi-colored playfulness and rotated ‘e’ of our previous mark—a reminder that we’ll always be a bit unconventional.”

“Unconventional” is displayed in the tilted “e” at the end of Google.

4  It’s Colors
color palette
Filling each letter with multiple colors, which was explored, would hardly be distinguishable in the small size it is often used. A distinctive color for each letter works best. The use of yellow in their “multi-colored playfulness” on the second “o” seems to be the weak design element.  I adore yellow/gold and the attention it gets in special circumstances, but it can often be challenging to distinguish at smaller reduced sizes. Notice on the image above, how difficult the white type is to distinguish on the yellow. This could use some finesse.
What they say:

“We adjusted and pushed the vibrancy of the red, green, and yellow to maintain saturation and pop.”

In 2008, when Walmart rolled out their new logo, their use of yellow was too light and made the mark hard to distinguish. They quickly refined by adding saturation to the yellow so it would hold up better.

5  It’s Their Visual Brand And Brand
visual brand
I appreciate Google’s transparency in all that they have shared and understand that this, as stated, is the brand they want to embrace.
What they say:

“…we hope this work will continue to deliver the simplicity and delight you expect from Google—wherever new technology may take us.”

related blogs
In 2013, Yahoo’s new logo rollout, also designed internally, was not well-received at all!
In 2010, The Gap’s new logo met with so much opposition, they returned to the old logo.
And…
In 2010, our blog on Google’s New Logo.