such

What does ‘such’ mean in the following sentence?

his visits gave his grandparents such pleasure.

I think it means : his visits gave his grandparents a great pleasure.

Can I say:
‘… such a great pleasure.’?

Not within the original sentence, Alexgowest.
‘Pleasure’ is uncountable there.

so it would be “such great pleasure” wouldn’t it?

Yep.

pleasure is a abstract nous which is uncountable and such is adjective which modifies pleasure.