Chaos Spawns are weird and wonderful creatures. Model wise G.W just give you a body and a crap load of bits and say "here, knock yourself out". In game they appear average, time to take a deeper look.
Know your slime bag
Chaos Spawn is a reasonably tough and strong model (S5 T5) with three wounds a piece. Not the fastest initiative wise or the best weapon skill. They are leadership 10, though they are fearless so this doesn't matter a huge amount. The negative for Chaos Spawn is they have no form of armour save and have D6 attacks, so you could roll a 1 or be shit hot and roll a 6.
Chaos Spawn also cause fear and have the rage special rule, so they will get