I hate to bad mouth this place as I guess they try hard, but it can't hold a candle to other museums of modern art I've seen. The displays were minimal at best; not minimalist, just minimal.
I sort of stumbled into the place and after spending an hour was sorry I took the time. Sorry 'bout that but it's the truth.
Unique Suggestions The first problem is to get oriented as the building layout is a bit confusing. Find out at the info desk what the primo display is and head for it. Then skitter out and head down the street for a Guinness.
Fun Alternatives From the museum you can see the Kilmianham Gaol. I suggest you keep going a block or two to reach it.
Not really a tourist trap, but it doesn't fit under "must see activity," the Irish Museum of Modern Art (IMMA) is free, so that's good. It is housed in the Royal Hospital Kilmainham with a sprawling 17th century garden out back. You would think the juxtaposition would be cooler, but I wasn't too impressed.
Also, I went in between 2 exhibits, and what was left was really unchallenging and sparse.
Unique Suggestions It's free, so at least you're not out some euros. I found the garden outside and the building itself more interesting than any art there. Try checking the website before you go to see if there will be cool-looking exhibits when you plan your visit: http://www.modernart.ie/
Fun Alternatives I enjoyed the National Gallery much more. It was much larger and also free (for the most part).