Versions of C#

1.0, 1.5, 2.0 (ECMA), 3.0

C# 3.0 is not currently standardized by any standards organization, but it is expected that it will also become an ECMA and ISO standard, as its early versions.

Features new in C# 2.0

• Partial classes which allow class implementation across more than one source file.
• Generics or parameterized types.
• Static classes that cannot be instantiated, and that only allows static members.
• Anonymous delegates.
• The scope of property accessors can be set independently.
• Nullable value types which provides improved interaction with SQL databases.
• Coalesce operator (??) which returns the first of its operands that is not null, or null if no such operand exists.

Features new in C# 3.0

• Language Integrated Query. 
• Object initializers & Collection initializers.
• Anonymous types.
• Implicitly-typed arrays.
• Lambda expressions.
• Automatic properties.
• Extension methods
• Partial methods.

Performance 

C# programs, like all programs written for the .NET and other virtual machine environments such as Java, tend to require more system resources than functionally similar applications that access machine resources more directly.

Platform  Microsoft's current .NET implementation is only available on Windows which allows us to design applications for Windows only.