I have read quite a few posts here about how awful berserker is....
In reality I think he is quite useful for resource raids, hero trials (even though they are largely useless) and pretty much anything.
His skill is great at destroying walls in raids, as well as targeting the highest HP hero while making defense almost impossible. He hits mediocre AoE damage but the stun, HP and defense reduction make it a hero that can be used quite successfully.
When I got my 4th berserker I created a berserker with 2 glory and evo'd him to Leo. His divine makes trials easy as it gives him 8 guards that act as mercenaries.
I will say though, I would not recommend him for aid or base defense, in both those areas he is quite weak.
Best advice, do not use him until you have him with glory (>1) and at least skill level 14 (uses 1.5 rage). After that enjoy him in raids as he can solo most noob bases in under 40 seconds.
Rank 17 and growing