I really think that you need to tweak the coding for raids.  There are sometimes some very insane numbers of monsters to fight against (i.e. 96 Giant Ants!).  Also, the rewards for killing the monsters are extremely inbalanced as well.  Sometimes you get 40 exp for a 6 hp monster and 8 exp for a 35 hp monster!  Also, you get like 130 gold for killing a bunch of monsters/a really hard monster, and like 500 gold for a 3-7 hp monster!

I'm sure that it'll be better once guilds are implemented, but you may really want to look into this nonetheless...