I used to hit the Tavern up pretty much every time I was on Mill, but looking back I'm not really sure why. It's not terrible, don't get me wrong, it's just that for almost every purpose there is a better spot to go. Patio, dance floor, strength of cocktails, and interesting people - within one mile you can find a place that will suit you better.
The thing that's nice about the Tavern is that it's generally less crowded than everything else along the ASU party corridor. It's also located right off the light rail which is really convenient for jumping off and grabbing a quick drink.
The back patio is cool, but gets PACKED so it can be tough to find a spot to sit and chill, and the front patio has so many smokers that you feel like you might as well just start smoking yourself and at least get a buzz on.
Meh - go here if you have a big group of friends going but not worth it without good people.