How good is the Google Scholar search Engine?
It's not so much "worse" as it is "different".  The base Google Scholar search uses a number of defaults that may not be optimal for a given search.  Check out Publish or Perish which uses the Google Scholar API and provides a number of additional means of searching such as citation counts, journal sorting, etc. that can be a lot more useful.  It also has an alternate option to use the Microsoft Academic Search API, which provides an alternative set of results.