There are lots of things that could be better, and I don't mean to imply that .NET's system is perfect. But the fact that List<byte> contains an array of bytes

There are lots of things that could be better, and I don't mean to imply that .NET's system is perfect. But the fact that List<byte> contains an array of bytes rather than an array of much larger objects is often important in practice, and dwarfs any complaints I might have. Not being able to use System.Void in .NET generics is an occasionally frustrating quirk, not a huge problem, in my experience. Indeed, it's quite easy to create a new type with no public constructors to achieve the equivalent result (and F# does this with the unit type).