Where 2nd Edition AD&D endows fighters with the ability to (at first level) swing a longsword in each hand, potentially doing 28 points of damagae in a single round without counting Strength bonuses, the 2nd Edition Priests handbook cuts a Priest's power in half. I didn't find a single Priesthood that allowed it's followers to cast spells from all spheres, and many were reduced in combat ability. The special abilities added often come at the cost of the Priest's ability to Turn Undead creatures.
In short, ignore the sample priesthoods, or at least give them more spheres and/or abilities, if you want your players to still be your friends.
The rest of the book is good. It provides mythos creation guidelines, so if you don't wish to play in Forgotten Realms or Greyhawk, you can create your own pantheon and mythology using the guidelines in this book.
The kits are not all that great, one of them even relying on the heavily flawed Martial Arts system from the Player's Handbook. But with a little tinkering, you can use them. Just about everything in here needs a little work, but it's not unusable.
It's a good reference for DMs who are creating their game world. For players, they will probably get little use out of it.