Very Fun City, Avoid Temple Bar
Me and my buddy (in our mid-20s) spent 4 nights in Dublin during St Patricks Day and we had a blast! The city isn't the biggest culture shock city, but if you're looking to go out and get blitzed every night, I think you found the right place. BUT AVOID the heart of temple bar. Beers are double the price, and you get the same experience as if you'd go to an irish pub in NYC. Venture a bit out, and walk further south from the river and you should be golden.
Insider Tip:Guiness factory A+ obviously and if you want something different to add to your trip, rent a bike at phoenix park. A great way to take a break from all the beer and partying and take a breath of fresh air. As I said in my review, if you want a great time for drinking walk more south of temple bar and you'll be on your way.
Fitzsimmons is the best overall bar in my opinion. Club in the basement, irish covers on the main floor, and rooftop bar. Good mix.