Postitives about Citrix:

• Client support – I’d be more surprised if you can find a platform XenDesktop isn’t supported on.  XenApp/XenDesktop uses the Citrix ICA protocol and therefore the Citrix Receiver.  There’s client’s for Blackberry, Windows 8, iOS, Linux and Android just to name a few.
• Integration with XenApp – A VDI solutions is not just about virtualizing the desktop but also about providing access to applications.  XenDesktop shares a lot of common backend infrastructure and features with XenApp.  You can use the same web portal for both your applications and desktops.
• Multi-Hypervisor support – Of course Citrix would like for you to use XenServer but you can also use vSphere and Hyper-V for you underlying VDI hypervisor.
• Flexibility – Citrix has integrated a great provisioning server into its offering.  The solution is designed to provide desktop sessions regardless of the underlying desktop technology.  You have a need to provide pooled physical desktops to a subset of users then no problem.  Just as long as you can install the client agent on the VM or Physical PC then you can use XenDesktop.
• Graphics Support – ICA is a very mature protocol.  Citrix has long given you the ability to run graphics intense application such as AutoCAD within a VDI session.  During HD video within a Citrix client is no big deal.
• Printing – Printing used to be one of the things I hated most about Citrix.  You can now reliably use most off the shelf printers within you VDI environment.

Negatives about Citrix:

• Troubleshooting – When Citrix breaks, it breaks hard.  Living without a support contract with Citrix is like walking without a net.  When I need to call them it’s usually not anything simple.
• Complexity – With flexibility normally come complexity.  XenDesktop is no different.  You have a ton of options for provisioning desktops, broker configuration, web portal options and etc.  If you don’t have a clear idea of what you want to accomplish it’s easy to overcomplicate your design.
• Lack of offline mode – Citrix ICA is a streaming protocol meant to be used with thin clients.  If you don’t have an Internet connection then you don’t have access to your desktops.  This should be a major part of your decision making process when considering VDI solutions in general as there’s really no ideal option for offline access.
• Management interface – There are simply some basic things you can’t do from the management GUI.  This makes the learning curve for the application steep as not everything is well documented.
• Talent availability – If you know Citrix you already know how high demand your skill is in the market place.  Because it’s good, because it’s complex and because there’s not a ton of 3rdparty documentation it can be really difficult to find talented Citrix administrators.  This can really be a major issue based on geography.