Lightroom is very quick & easy/intuitive. Better suited to global work, batch adjustments (very useful for studio settings or where light conditions don't change), it has incredible and effective catalogue/archiving/seach features. Also one important feature is the fact that you can have many different "virtual" copies of the same file (such as: Original, B&W1, B&W2, ... B&W.n, SplitTone1, SplitTone2, ... SplitTone.n, Color1, Color2, ... Color.n, Crop1, Crop2, ... Crop.n and such...) w/o loosing disk space for each copy. LR isn't a replacement for PS, whereas PS isn't a replacement of LR; they complete each other pretty successfully.
Regards,
Loris.