Futuresex/ Lovesounds [Explicit Content] (2 Lp's)Music critics and highbrow listeners may look down their nose at Justin Timberlake, doubting that the celebrated former N'Sync leader is good for more than light, frothy dance pop. Timberlakes's sophomore effort, FUTURESEX LOVESOUNDS, should make both camps rethink that stance. While the album certainly sets out to entertain, it's also full of ambitious, well constructed grooves that prove the superstar is serious about getting down and dirty. The