Pierre Boulez's glory days as a composer are behind him: his best, most radical music (Le marteau sans maitre, Pli selon pli, Le soleil des eaux) dates back to the 1950s and '60s. As a conductor, however, the erstwhile enfant terrible has eased into the role of sagacious partisan, a sympathetic interpreter of contemporary music who can guide listeners through the thickets of the unfamiliar. His interests may shift from Mahler to Debussy, from Stravinsky to Schoenberg to Scriabin, but his conducting is invariably lucid and precise--so much so, in fact, that his approach has been criticized for being too clinical, for emphasizing structure over emotion. For much of the 90s, his concerts with the Chicago Symphony Orchestra and his erudite lectures were hot tickets, but attendance at his events has dropped--maybe the novelty has worn off a bit, though the CSO's rising ticket prices and marketing strategies are probably just as much to blame. But Boulez's return is still much anticipated. In the next three weeks he'll lead the CSO in programs that feature a Haydn symphony (highly unusual for him) and Berlioz's Requiem (a highlight of the season) as well as overseeing a potpourri of chamber works by himself, Hungarian avant-garde veteran Gyorgy Kurtag, and CSO resident composer Augusta Read Thomas. In this week's concerts he'll pay homage to two master impressionists (Debussy, represented by his penultimate work, Images for orchestra, and Ravel, by Le tombeau de Couperin) and one of the contemporaries they overshadowed (Albert Roussel, by his neoclassical Symphony no. 4). If you haven't heard Boulez conducting Debussy, with whom he feels a strong affinity, then you haven't been privy to that composer's essence. Friday and Saturday, November 29 and 30, 8 PM, and Tuesday, December 3, 7:30 PM (Debussy et al); Thursday and Saturday, December 5 and 7, 8 PM, and Friday, December 6, 1:30 PM (Haydn et al), Orchestra Hall, Symphony Center, 220 S. Michigan. 312-294-3000 or 800-223-7114.