Unlike some of it's counterparts, O'Gara's & Dublins for instance, Keegans is relatively laid back & small. Though they have great acoustic sets & live music all the time, and you do get the U crowd, Keegans tends to attract an older, more sophisticated partying drinking rowdiness :-)
The beer is tall, and they have a great selection, as well as some fair wines. The food is great actually, for pub food, and I've gone there for brunch on occasion because it is so good.
The atmosphere and relaxed Irish spirit is the best thing Keegans has going for them though, and they do that well.