Crammed one on top of the other, the little local places serving everyone's favorite grilled meat on a stick will make you feel like you've stepped out of modern Tokyo and into some mythical parallel dimension of exactly what people who have never been here expect Japan to be. Friendly staff, don't expect any service whatsoever in English. Take the Japanese friend assigned to you upon processing through customs and have them help you order.
The building itself is a beautiful example of architecture. And this building is a one-stop shop of anything bureaucratic. Literally any government function you can dream up can be found here. Very popular tour destination in the heart of the skyscraper district in Shinjuku. But if it's a view you're after, Roppongi really is a better bet. Especially since there is usually a pretty lengthy line for the elevator up to the top.
If you're looking for a vintage Irish pub, you'll want to take this one with a grain of salt. It's owned by Sapporo. Nevertheless, they have decent pub food for good prices, and a few of the import beer favorites. If you're looking to get a seat, or even standing room for more than three people on a Friday or Saturday, you'll be happier going elsewhere. The clientele is a more balanced mix of foreign and Japanese than a lot of other similar pubs around town.
The food was excellent and the portion sizes for the set course menu for a large group was very generous. Classic tex-mex with fabulous and irresistible tortillas made from scratch in-house. Unfortunately, the drink service was pretty slow. But they have a good selection of moderately priced imported beers. And an extensive selection of cocktails: margaritas to daquiris and their own signature drinks. Lively atmosphere but a location not that easy to find for newcomers to the area. Reservations are highly recommended as the wait can be up to 45 minutes on an average weekday.