We just spent a week completely replacing our hand-built, completely custom Fire Hazard, Citydash and Undercover sites with an off-the-shelf CMS.
The new sites are live now. Technically they're not as good. Squarespace doesn't support HTTPS, so (due to HSTS on the old site) the URLs are a bit weird. The images aren't as well optimised, so they load slower. While we have more pages, the design for each is very similar. And we no longer have proper source control - Squarespace doesn't have any form of checkpoint and rollback.
And it wasn't like it was a small piece of work to do, either.
But we had to do it. Because the old sites, while great, never changed. Updating them took too long, and only one person in the company could do it at all. This conflicts with who we are as a company. We're Fire Hazard. We move quickly, we move dramatically, and we don't wait for anyone. If someone has a great idea for a new game, I want it live on the site that night, not "in a couple of weeks". And all the lovely things people are saying about us should be up on the web, not buried in a [win] tag in my Evernote where nobody will ever see them.
So if the new site seems like a downgrade, it's not. We're getting bigger and we're getting faster. And, ultimately, we're here to make exciting experiences, not websites.