It is definitely the most extensive Arabic-English dictionary out there, but be warned that it is concerned primarily with Classical Arabic. Thus people doing extensive reading of the Qur'an, Hadith, Poetry and medieval texts will find it of great use. However, for those concerned with modern literature and media, it is out of date and a bit too cumbersome (stick with Hans Wehr).
Still it's a great resource and the probably the next best thing to لسان العرب.
x-posted to arabic