Yes, all 4 guardians dropped Primal Weapons which were the best weapons in the game for the longest time. Even after some expansions they were still the best around.

If you killed all 4, the Sleeper would awake and wreak havoc, but this wasn't even close to the bad part. You would no longer be able to get Primal weapons after awakening. Usually a guild that was completely geared out would do this to set themselves apart from the rest of the server or a guild that wanted to screw over everyone. Due to the very high amounts of drama this caused about 95% of all guilds that woke the Sleeper were destroyed/disbanded within the first 2 months it was that devastating.

(they later created similar items in the zone about a year later that had the same stats though)