A ‘fun’ topic.

[Seymour5]

That is so fun!

Is it? I thought something could be so much fun, or so funny, but ‘so fun’? Does it sound strange to anyone else?

It does indeed.

I hate it

So annoying! So not fun!

(sorry!)

So much fun sounds much better

Or “such fun!” As said by Miranda’s mother

According to the OED, 'fun' is both a noun and an adjective, so I don't see any reason why 'so fun' would be incorrect.