I agree with stimpy's summation.

The "old city" portion of Prague is extremely well-preserved and/or restored and has a unique architectural aesthetic if you're primarily used to western Europe. It also has an old Jewish quarter (though very, very few Prague Jews survived the Holocaust) that gives some insight to Jewish life in Europe prior to WWII. There are also some significant and quite beautiful arte nouveau buildings.

It has some very, very good restaurants (though avoid the more touristy ones -- the Three Ostriches is worth seeing, but our meal there was medicore compared to other restaurants that we visited. I had roast goose for the first time in Prague -- ummmm, my mouth is watering just thinking about it.

Absinthe is legal in Prague -- it tasted like cough medicine to me, but at least I can say that I tried it. Prague is also famous for some very good beer.

As others have noted, Prague is frequently awash in tourists. We went during shoulder season (late April/early May), and parts of the city were quite crowded. However, it was still possible to get a sense of medieval Prague, and we had no trouble getting into restaurants, cafes, etc.

We loved Prague and, indeed, I know very few people who have been there who don't feel the same way.