What is most valuable?
You can get it downloaded and installed for free. It allows you to do more with less. It's easy to use and simple to configure. There are hardware vendor specific builds of the software, increasing visibility and manageability of the product.
How has it helped my organization?
We have less physical servers to monitor and put under warranty.
For how long have I used the solution?
10 plus years in various forms as GSX, ESX and now ESXi.
What was my experience with deployment of the solution?
Deployment options are varied with ESXi, so depending on what you're trying to achieve within your business.
What do I think about the stability of the solution?
Due to the multitude of configuration options, you can occasionally experience compatibility issues with 3rd party storage vendors such as NetApp which recently had a known issue with NFS reporting all ports down.
What do I think about the scalability of the solution?
Never encountered any scalability issues with this product. It is truly enterprise.
How are customer service and technical support?
Customer Service: Good to excellent.Technical Support: Good to Excellent depending on what engineer is assigned to you.
Which solution did I use previously and why did I switch?
I have tried other hypervisor technologies including XenServer, Hyper V, KVM, Parallels and virtual box. They all do the same thing, but ESXi has been doing it better for longer.
How was the initial setup?
Exceedingly simple setup. You can make it more complex depending how truly enterprise your needs are, like stateless implementations of ESXi.
What was our ROI?
Reduced Electricity Bills, reduced hardware and warranty costs. Reduced server implementation time. Increased management and availability of corporate services.
Which other solutions did I evaluate?
Not on this occasion but I have assessed other hypervisors.
What other advice do I have?
Assess why you think virtualisation is the answer to your problem. Research hypervisor choices, perform Proof of Concept exercises with those products you choose to assess and most of all think about the legacy of what you're doing. i.e. what do you want to leave behind?