Ugh, if you're over the age of 22 just do yourself a favour and walk on by.
If however, you're a young Uni student or wishing to relive your days as a frosh than you'll probably have a good time. It's loud, full of rowdy youth and has a decent brew selection and a few nice patios.
This place is always packed despite its enormity. To my surprise there also always seems to be a big line-up out front, although I can't for the life of me understand why anyone would line up to get into this place.
Although, to be fair, I am writing this as someone that is a decade too old to enjoy a place like the Maddy. I would happily avoid it but occasionally a friend who has gone back to school at a more advanced age is taken in by the reputation of the pub as a college hot spot. They then proceed to organize a birthday party, inviting all of their 30+ year old friends to join them in this cavern of obnoxious drunkenness. We all wonder why they have invited us there and bitch amongst ourselves about spending a night with the frat kids. Of course none of this is conveyed to the oblivious friend who planned the ordeal. In the interest of friendship we begrudgingly attend and try to yell out a conversation over the noisy backdrop, all the while feeling a little bit of pity for the friend that just hasn't caught on to age-appropriate hang-outs.
Don't let this be you. If you're an adult with a social circle above the age range of 18-22, invite your friends to join you somewhere else.