"Back To Baldur's Gate is essentialy a "Harder Enemies" patch, with more
than 130 enemies changed!
These have new Stats/Skills/Scripts to give the player a
much more tactical/satisfying gaming experience."
Also note that the mod requires "Dark Side of the Sword Coast".
I've tested it a little, and so far it's not bad but seems it hasn't gotten the playtesting of SCS yet.
If you try it be sure to report your experience back to the author. From reading his forum I get a strong impression he would appreciate and be very receptive to feedback.