is c # – 86 a good index of maintainability?

I was wondering if 86 is a good index of maintainability in the Calculate code metrics option in Visual Studio 2016 or not.
If this is not the case, what tricks can you do to lighten the code?
I actually have classes whose logic is quite complex (I'm building a compiler for my own programming language in C #) and I do not know if I can simplify some switch statement or other things.
Below my least well indexed method among a solution containing 10 projects:

static public void EmitExpression (this ILGenerator it, Expression expression, Member scope)
{
switch (expression)
{
Name of the case NameReference:
il.EmitName (nameReference, scope, EmitMode.Load);
Pause;
numberExpression numberExpression box:
il.Emit (OpCodes.Ldc_I4, (int) numberExpression.Number.Value.GetWholePart ());
Pause;
StringExpression box stringExpression:
il.Emit (OpCodes.Ldstr, stringExpression.String.InnerText);
Pause;
invokeExpression invoke box:
if (il.EmitName (invoke.MethodName, scope, EmitMode.DoNotEmit) ?. Info is the MethodInfo method)
{
foreach (expression argument in invoke.Arguments)
il.EmitExpression (argument, scope);
il.Emit (OpCodes.Call Method);
}
Pause;
caseExpressionExpression operation:
il.EmitExpression (operation.FirstOperand, scope);
il.EmitExpression (operation.SecondOperand, scope);
il.EmitOperator (operation.Operator);
Pause;
}
}