Writing a review for a Server is incredibly hard - one person's impression on the Operating System will be totally different to another, purely because both administrators have asked the software of totally different roles.
If you have used previous Windows Servers, 2008 is not massively different in terms of the UI. There are subtle differences here and there, such as the Event Viewer has had a massive overhaul, but the core components are the same.
Instead of replacing features, Server 2008 typically improves upon them, and adds new technologies. R2 pretty much refers to Revision 2 of Server 2008 - so it includes bug fixes and even more updates. It also has another level of domain & forest functionality (2008 R2), which implements the Recycle Bin for users.
The Standard Edition of Windows Server is the lowest level of Server available, so there are some features not available (Certificate Authenticator in Enterprise mode for example). Make sure you check with Microsoft before purchasing the server version is the correct one for you.
This version includes the following server roles:
Active Directory Certificate Services
Active Directory Domain Services
Active Directory Lightweight Directory Services
Active Directory Rights Management Services
Network Policy and Access Services
Print and Document Services
Remote Desktop Services
Web Services (IIS)
Windows Deployment Services
Windows Server Update Services (WSUS)
This makes this version a perfect candidate as a member server of a domain, or as a domain controller, a web server.....the operating system is amazingly multi-functional, and from my experience the roles are mostly integrated very well. I think Windows Server is a solid foundation for a business network needs.