St. Louis Post-Dispatch Felix Mendelssohn The Complete String Quartets Cedille Records 90000 082 (3 CDs) May 19, 2005 By Sarah Bryan Miller Felix Mendelssohn (1809-47) left the world with just seven completed string quartets and four unpublished movements, but they are marvelous pieces that somehow don't get played (and, thus heard) enough.   The Pacifica Quartet - violins Simin Ganatra and Sibbi Bernhardsson, viola Masumi Per Rostad and cello Brandon Vamos; they're Faculty Quartet in Residence at the University of Illinois - have just taken steps to amend that unfortunate situation with their splendid new recording of the complete works for string quartet.   The Pacifica play with verve and understanding, and exhibit an appealing devotion to the spirit of these gorgeous pieces, which run the gamut from youthful to very late in Mendelssohn's short life. Known primarily for their work in contemporary music (the Pacifica has a real allegiance to commissioning and performing new works), they bring a freshness and emotional commitment to these appealing compositions. Along with fine performances, the recording has superb engineering from the ever-careful folks at Cedille Records; the sound is appropriately warm and rich. It's also nicely priced, with three discs for the price of two.   This box sets a new gold standard for performances of Mendelssohn's string quartets. If you have an interest in his chamber music, the Pacifica's version would make a natural first shopping stop.