I like the CE Ferulic, but I think it's a bit strong for my skin. It tends to make me have "purge breakouts", which are then followed by a glowing, clear complexion. I'm thinking of switching to the Serum 10, which is milder, and the formulation has the magic ferulic acid. I've read the combination of C and ferulic acid maximizes the free-radical blocking effect of sunscreens by an eightfold.
I've also used their SPF 20, a broad-spectrum mineral-based block which doesn't leave a chalky cast to your skin. I've read it's still not as good as European approved sunscreens, like LaRoche Posay's, which contain a more-effective sunscreen that has yet to be approved by the US FDA.
I'm currently awaiting samples of their Phyto+ from an eBay seller, a good place to get Skinceuticals at a steep discount. Sunscreen or no, it's been a particularly non-foggy Bay Area summer, and I've become a giant-spotted melasma monster. I'm hoping the kojic acid will make me pristine and coveted porcelain again.
I still can't help but think my skin was better before I started with all this crap, but truth is I'm in my 30's now. Soon starts the inexorable flesh sliding off bone that no expensive serum will halt. I certainly hope I can find someone superficial enough to love me before the grotesqueries of my credit rating prevent my face's being fishhooked and sutured into a simulacrum of youthful loveliness. Save me, Skinceuticals serum!