Sorry to hear that Adrian.
Quite often the first dram out of the bottle is, for some reason, very disappointing. Give it a week or two and try again once the air has had time to work its magic.
Glenfiddich 18 is a good whisky and that's why it's popular. I think it and the 15yo are probably the pick of the more affordable 'fiddichs. I'd be surprised if it continued to disappoint, but if it is not for you then that's just the way of things. Hopefully though, you'll find it to your liking as time goes on.