I want to preface this with the fact that I don't know if my review is fair. I believe Pantheon is a good company, and I am the wrong customer. I am a business owner with an ability to build and maintain my site, however, all of my skills come from me following tutorials online. - So take this for what it is worth.
Pantheon requires a high level of understand, not basic. Virtually anytime I want to implement something I've learned elsewhere from a tutorial online, I am immediately confronted with the fact that Pantheon runs on nginx, so most tutorials found elsewhere are of no use.
Multidev always have 504 errors. Which requires you to refresh your page a couple of times to get it to clear. - This is always frustrating, but only happens on multidev and not live.
Support is hit or miss. I've been on support chats with some incredible people on Pantheon, and they will go above and beyond to help. They're patient, provide me with suggestions and documentations, and walk me through what I need to do with clear screenshots and explanations.
However, other times, I am met with someone who is not interested in supporting me, is not patient, and does not want to clearly explain things.
Their staging platform is too complex and there are always issues. After using Pantheon for a few years and struggling to find a seamless was to commit changes, I hired a developer with Pantheon experience, and he too was met with complex issues just committing a staging site to live. - So I believe the complexity does carry over a little bit to those with more skill than me.
I believe some of my most frustrated moments in the last years have been a result of me simply trying to publish changes to my site, only for Pantheon to throw issue after issue my way.
The price is also too high. Once you reach 30k page views, the cost goes from around $40 to more than $200. Comparing that with WPX.net, a company I have my eye on switching over to, the price bump would go from $25 to $50 once you reach that mid-tier. - Maybe I am comparing apples to oranges here because Pantheon does a bit more, but their added features are not justifiable by someone who just has a simple Wordpress business site. Review collected by and hosted on G2.com.