Pros
I have to say that I'm surprised by the negative reviews here to the point where it seems like those people were working for a completely different company. As another reviewer mentioned, the complaints of long hours scream inexperience. Long hours and VFX are synonymous and, outside of pilot season, CoSA's schedule is about as close to a regular desk job as you can get.
Also, I find management and the supervisors to be extremely courteous, hands-on people. Rarely does a day go by where at least one person doesn't explicitly thank me for my work. I have NEVER had another job in any field where I could say that. Not even close.
And the parking complaint? Really? There is free street parking EVERYWHERE. Try getting a job in Santa Monica for a while and then we'll talk.
Besides all that, you get to contribute to some really high-profile shows and there is a lot of opportunity to learn from some amazingly talented people around you. For young artists especially, that is a huge, huge plus.
Like many other things on the internet, I'd say take the negative reviews with a grain of salt. Some seem to be holding a grudge and others certainly don't seem like they knew what they were signing up for when they decided on a VFX career.
Cons
It's hard to think of any. There are some growing pains in the pipeline for sure, but things generally work very well and problems are addressed by the development team very quickly.