I've been to O'Sheas a few times now and it has its good and bad points, labeled an Irish bar it undoubtedly has a few novelty Irish touches (the jerseys, a painted harp) but the lack of any Irish staff or of English speakers made it feel less authentic, but I guess that's just my opinion.
There is a wide selection of food on the menu but it is slightly misleading with terms for example, once I ordered Bangers and Mash, (made with authentic Irish sausage) and I got one hot dog and mashed potato. In this sense the food is underwhelming and you could be left waiting a little longer than average in Nicaragua.
Also the bar's location can be a double edged sword as it is located on calle la calzada (the main tourist strip in Granada), which ensures that it is mostly busy but ensures that you will be heckled PERSISTENTLY by people selling hammocks, whistles, cigarettes, flowers, paintings, mariachi bands or kids just asking for money which starts to become annoying if trying to relax.
Also, this may seem pedantic and is probably a cultural difference as the staff are Nicaraguan, but the waiters seem a bit too pushy about cleaning the table after food, I ate there one time (another occasion) and I was just finishing some food and one waiter cleared half the table and stood behind me and waited for me to finish so he could take it, the same applied with beers, a little too eager to take my drinks away, maybe trying to look busy or maybe cultural differences I'm not sure.
But to end this on a positive review, the resident gringos and Nicas of Granada take O'Sheas for what it is, it's fun, noisy and occasionally hectic but is often where the party is at.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.