I like the new monster lair system but I feel it could really be better optimized. They are both too easy to destroy, don't produce that many monsters, and scale too fast.
Currently from what I have seen they look like this...
Step1: A single weak monster is spawned and will attack nearby units.
Step2: The first monster starts to wander around a bit more, and a small group of tougher monsters is spawned.
Step3: A even tougher monster is spawned etc etc
The problem with this is that monster lairs are ridiculously easy to destroy off the start, they don't really produce that many monsters, and don't really feel like a lair. Also the next wave of monsters can spawn suddenly and take you by surprise, they can be really dangerous and very newb unfriendly.
I would suggest something like this...
Step1: A single immobile weak unit is spawned.
Step2: A stronger immobile group is spawned on the lair and the weaker group starts to wander around.
Step3: Another weak group is spawned and starts to wander around.
Step4: Back to Step2
This way the really tough monsters don't attack players to quickly but they are there if you want the challenge. Also more weaker monsters will continue to spawn for longer so you don't run out of weak monsters to farm quite as quickly. With tougher monsters sitting on the lairs the lairs are harder to destroy.
Also as I mentioned in another thread the tech required to recruit from monster lairs is way to high up the tech tree, Darklings are tech 4. The first reliable way to get diplo capital is tech 5!