Is Abu Dhabi worth a visit for a few days if you’ve already been to Dubai?

BrianO asked: Possibly going there next year – direct flight from Dublin, Ireland with Etihad Airways.

Would like to do some snorkelling / scuba diving, jet-skiing, more sandboarding. Seems to be a nice city with some historical sites, beaches and man-made islands.

Nightlife aspect isn’t too important. Loved Dubai too when I was there 2 years ago.