I could be wrong and I'm not on the rating committee, so take everything I say with a grain of tequila and salt.
My thoughts:
1) Poison - 40 poison throwers seems like a lot for the amount of monsters that OFCC brings out
2) 3 Big Monsters - 3 itself doesn't bother me so much as the size of two of them. Over a 1000 points in monsters and 950 of that in two of them. Yes, there are armies that will have a good chance to deal with them as they have enough shooting, or chaff to give them time to deal with them. But many armies don't field shooting or chaff, so having those in your units (units that the Lizards choose based off movement) early or before you have a chance to adjust (ambusher) can make for a very sad opponent. Now with that said ambusher is going to delay how many rounds you get to use that unit or where it shows up, so that could cause a benefit for the opponent.
3) Your two big units are not death stars per se, but both are killy in their own right and hard to dislodge points. Im ok with these two units actually, but just stating overall thoughts.
4) 5 speed bumps that can kill. Unlike most speed bumps in armies, yours actually can do a decent amount of hurt prior to dying. And the fact that there is 5 of them which is more than most armies field for redirectors/chaff it will make it hard to get to grips with the actual points of your army. It will also allow the user to setup the favorable matchups for the big beasties.
Perhaps I overreacted, but I would still probably rate this 3.9-4.2 currently. Especially based off some of the other lists posted that seemed more friendly.