Line 5 has 2 if() functions, the first one asks, "if it's not audio, series,music vid or consert, is it standup?" and the second on says, if it's standup, do one thing or the other depending on the contents of [season]. the end of that season if() question has no closing bracket, and I'm also pretty sure there's a closing bracket short at the end too.
Try the one below and see if that works any better, changes highlighted in red:
If(IsEqual([Media Type], Audio),[Name] - [Artist] - /([Album]/) // Rating: [Rating],
If(IsEqual([Video Type], Series),If(IsEmpty([Name]),S[Season]E[Episode]/ (NP:[Number Plays]/),S[Season]E[Episode]/ (NP:[Number Plays]/) - [Name]),
If(IsEqual([Video Type], Music Videos),If(IsEmpty([Artists]),[Artist] - [Name],[Artists] - [Name]),
If(IsEqual([Video Type], Conserts),[Artist] - [Name],
If(IsEqual([Video Type], Standup),If(IsEmpty([Season]),[Name]/ (NP:[Number Plays]/),[Name] - S[Season]E[Episode]/ (NP:[Number Plays]/)),[Name])))))
-marko.