I played seige mode for the first time last night and after about 5 games. I must admit that my first impressions arnt that high 
I believe this is partly that I'm not very good at the mode, and/or the fact I was with Randoms against seemingly organised teams.
When playing as a zombie it takes most of your time just getting to the area with the survivors to just get insta killed. Then after a long respawn time later your in the last half of the game.
I don't know why but the enemy teams agent was regenning health but the agent we had wasn't?
When it was our turn everyone seemed to be trying to control the agent leading to conflicted path finding which left him wide open.
However in another match the zombies started closer than we did so by the time we got to the agent the zombies were all over him. And he was pinned in the corner by 3! Whoppers so basically just about instantly died.
I would say its unbalanced but I lost easily on both teams, so I just need more practice I guess.
But like predator mode, I think the time limit is too short, and better zombie movement is needed.
When your playing as survivors you attack wherever your aiming the camera, zombies have tank controls and only attack the direction their facing which doesn't help since turning as a zombie is deadly slow.
Javo is a slight improvement but more or less a similar story.
Random observation:
Why do so many players in mercs, onslaught, survivors, predator and seige randomly kick you for no reason?
I dislike joining games sometimes because when I join a lobby I just get kicked randomly? Why open a lobby if your going to keep it private? That's Wht private slots are for!

I believe this is partly that I'm not very good at the mode, and/or the fact I was with Randoms against seemingly organised teams.
When playing as a zombie it takes most of your time just getting to the area with the survivors to just get insta killed. Then after a long respawn time later your in the last half of the game.
I don't know why but the enemy teams agent was regenning health but the agent we had wasn't?
When it was our turn everyone seemed to be trying to control the agent leading to conflicted path finding which left him wide open.
However in another match the zombies started closer than we did so by the time we got to the agent the zombies were all over him. And he was pinned in the corner by 3! Whoppers so basically just about instantly died.
I would say its unbalanced but I lost easily on both teams, so I just need more practice I guess.
But like predator mode, I think the time limit is too short, and better zombie movement is needed.
When your playing as survivors you attack wherever your aiming the camera, zombies have tank controls and only attack the direction their facing which doesn't help since turning as a zombie is deadly slow.
Javo is a slight improvement but more or less a similar story.
Random observation:
Why do so many players in mercs, onslaught, survivors, predator and seige randomly kick you for no reason?
I dislike joining games sometimes because when I join a lobby I just get kicked randomly? Why open a lobby if your going to keep it private? That's Wht private slots are for!