Make sure you get into the Heritage Lounge, the hotel's concierge lounge...fireplaces, chandeliers....absolutely opulent.
Have a drink in the Horseshoe Bar. It is a right of passage for Dublin students as they graduate from college. Small, quaint, cozy. Be advised you may be carded to get back into the hotel after a great day of Dublin sightseeing. It is the place to be and be seen among the socials of the city. No worries, guests get preferred attention.
Another tip, look at the Platinum buy-one-get-one free weekend night offers for Platinum Elite members. It is valid here, one of the few European hotels that participates. A real plus for being an Elite member.