A Volcano Planet is a particularly inhospitable single biome planet. The air is choked with smoke, the ground is scorched and cracked (and prone to earthquakes), and the water has been secretly replaced by rivers of molten lava. There's big nasty mountains, and they look like they're gonna blow. Regardless of whether or not there's a bright center to the universe, you don't wanna be here.
This is a lot more Truth In Television than many of the other single-biome planets. Io (moon) is a lot like this, Venus has gone through repeated stages like it (every time the subterranean pressure builds up enough), and the first few hundred million years of any planet's life may look a bit like it too.
That said, in the realistic version, there's no oxygen (because there's no plants), and there's probably sulfur, carbon dioxide or far worse in the atmosphere. You don't want to breathe anything native to this planet. The temperature is at least a few hundred degrees, and may be more than a 1,000o. This place feels like a Death World.