What is bad about geothermal energy?
Availability and price.
The only major negative to geothermal energy is the fact that it's only actually available in very select places. Iceland benefits tremendously from geothermal because the entire island is an active volcanic site. The problem is that most of the world isn't sitting on a volcano.
The second minor downside to geothermal energy is that in some cases it is costly to build geothermal power plants. In many cases, however, they can actually be very cost effective, especially in areas where using coal, oil, or alternative energy sources like solar and wind are unfeasible.
The vast benefits of geothermal definitely outweigh the cons, but they're only available to a few places in the world. That said, the United States has a source that could be very significant. Paranoia surrounding Yellowstone National Park erupting (it's a supervolcano) soon led scientists to see how to prevent it.
They figured out that if they pumped water into the volcano it would both reduce the possibility of eruption and provide enough electricity to power the entire nation. Completely sustainable power which would be completely affordable in the United States budget. Steps would have to be taken, however, to make sure that the natural beauty of Yellowstone wouldn't be affected at all by the our exploits.