How good is the Google Scholar search Engine? I've been using Google Scholar search engine for a while in order to find scientific articles for my master thesis, but I've come to notice that the search algorithm is not as good as the real google search engine. 

I feel that Scholar requires quite specific search terms in order to find the right articles. Does anybody share my experience and is it true that the Google Scholar search engine is worse at searching than the main Google 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.