While the Warwick sisters' voices were no doubt of similar quality, their styles were vastly different. Dionne was a master of subtlety while Dee Dee wasn't afraid to ignite the fiery inferno of flaming DRAMA. She never overdid it though. She knew how to use her instrument and applied the gentle touch when appropriate. Just check out "Yours Until Tomorrow" or her country-soul recording of "She Kept On Talking" for a fine examples of that.
For "Foolish Fool" to become such a stunning recording it needed a well-crafted song (by Ed Townsend), a delicious arrangement (by Rene Hall), skilled and creative musicians, and of course a vocalist who not only could SANG but who can interpret a lyric. In this case we have an incredibly sophisticated symphonic production that still manages to have a cookin' soulful groove. The instrumentation on this record is essential in making this the case.
The guitar in the intro sets the tone, letting the listener know in no uncertain terms, it is PURE SOUL that will be the driving force on this record. Sadly the guitar intro is drastically shortened in the single version of the song (I've posted the LP version here). It's almost like the guitar is taking you by the hand saying "Hey there, let me lead you to this really cool record you're about to hear." I also need to give a nod to those drums. I am such a SUCKER for the climactic use of drums in 1960s NY productions. They makes those records seem so much larger than life.
Give this record a listen and if you like it, consider listening to Dee Dee's entire Mercury/Blue Rock sessions collection. It's one of my favorites.