Is the medication ceftin (cefuroxime) a mild or major antibiotic for sinus infections?

That depends....: Ceftin (cefuroxime axetil) is a 2nd generation cephalosporin antibiotic (there are 4 generations now). It is commonly given for infections across the lungs, sinuses, gut, and skin. Mild or major, depends on perspective but overall i would say that antibiotics are over-prescribed. The key at this point is to finish the course you were given.