The star rating system in Spain is very complex because there are seventeen regions in Spain which adopt their own standards for hotel star classification. So unless you know the exact specifications for each region the star system is not very helpful.
For this reason the star rating system for hotels in Spain is not particularly useful.
However the star system does give you a very rough indication of the quality of the hotel.
It is a good idea to look at the characteristics of each hotel rather than being too influenced by the number of stars.
For example a hotel which is totally on the ground floor could not get a good star rating because it has no lift although a lift is not necesary.