WebMapSolutions shares an interesting entry named Is Google Maps GIS Lite?
From their conclusion: "When compared to the expensive, but well-polished products of ESRI, they may seem a bit rough in some areas, but they are also considerably cheaper or free to use as well. Everything is a trade-off. The hardcore GIS capabilities are not up to the same level as others such as GeoServer or ESRI, but then again that’s not what Google is shooting for either. They seem to be happy helping to expand the lighter, much larger-scoped public side of geospatial (which do cover a lot of use-case scenarios). [...] The direction is not towards traditional GIS work, but more into expanding the geospatial capability and usability on mobile devices. [...] Google kicked the old GIS world in the pants in 2005. They have plenty of expertise and money on their side to do it again."