In my experience, VMWare is great and has a nice GUI, which lead to early adoption. BUT: it has licensing fees for each copy. This can be a big bummer for companies like PayPal that have a fleet of servers - much easier to replace to replace all the VMWare installs and get rid of licensing costs to switch to an open-source VM solution.

At the same time, I could be that OpenStack's API is superior to VMWare's. With a fleet of servers, you want to automate as much as possible - meaning that at the end of the day, API trumps GUI.

Their pricing has gone up while the rest of the industry is trending down. This wouldn't be so bad except that most of their tools are very enterprise-y – clunky APIs, odd gaps in tooling, etc. Basically the hypervisor is developed by the A-team but the management tools and even components like the HA manager were obviously second-tier – big, convoluted snarls of daemons for something which should have been clean, simple and trustworthy. (i.e. I spent a few weeks on the phone attempting to convince second or third-level support that the HA system should also pay attention to the heartbeat checks rather than ethernet link status when deciding whether to use a network connection. The techs I talked to were under the impression that this was how it worked until I proved otherwise…)

I stopped supporting it in 2008 but at the time it was already apparent that they were trying to milk large companies rather than stay competitive – and that was before the price hikes.

Well nothing specifically is 'wrong' with VMWare, except for their notoriously terrible pricing... as in you might want to do the math and just buy more physical hardware and not virtualize anything unless you can get 10:1 or higher instance scaling out of the VM servers.

At one point VMWare was actually pricing things by memory used, not processor core counts.

Price most often.

Licenses for the top-end ESXi run $1000 - $3500 list per socket [1]. If you have a large deployment you're going to be inclined to go for the top-end license in order to support distributed switching and granular control over storage/network traffic.

Licensing costs.