A great way to see some key sights and get your bearings in the city. The Red Line was very good, not to far between stops, lots of options, runs frequently. The commentary cuts out frequently, often cutting off the "fun fact" you're about to learn. All-in-all, recommended though.
The blue line however is a different story. Very few stops, huge distances in between them, you will spend a lot of time sitting on a bus, stuck in traffic, to not really see anything. Skip it! Stick to the Red Line!