I have played extensively, and have found its not the Lancer that's "OP", its the way the damage is done. seeing as how almost every common unit on the game field easily qualifies as a Biological unit for the first twenty to thirty minutes.
Just gonna grab this some bit as a qoute because I think it highlights some points I wanted to make.
I've noticed too that many will simply go for stalker lancer, and others are put in an awkward stance, they either go for a biological unit like the beetle or raider, or blinklot, but they are highly vulnerable to the lancers, if they go ranger of goliath they are then gimping themselves to everyone else (although I've never had any luck with the goliath personnally).
I think I would suggest a bit more combat diversity in the ranks of the mercs, the lings seem okay, I feel as if zealots are lacking untill charge/more upgrades, but mauraders are ussually the early game IWIN button.
Also it seems to me that air itself is at a disadvantage, any unit with a form of splash has the potential to wipe out an entire air army, despite upgrades in some cases, the way in which air stacks on itself can become more of an obstacle than the enemy your facing.
I personnally think that the 3rd tier of mercs (reaver destroyer, goliath) were a bit of an odd addition, I'm not sure why it was they were put in exactly, I think I would've prefered more race specific units, perhaps mini ultralisks? hydras, immortals, reapers.
Also, has anyone even seen a game with a queenfestor? I got one out once but that was back in beta and I died before it was of any use.