Re: C# vSphere client was - how shall we put this? – bad. Just bad
It's not fast, but it does work decently, even without a vSphere server if you have to manage a single simple ESXi. But being C# it's mostly Windows only.
I don't understand why they didn't make it in Java (which they use elsewhere) - I hate Java, but if you need a cross-platform desktop application is one of the very few choices. and probably the easiest one. C++ and cross platform widget library are a more complex solution.