There aren't a lot of options in Karlovac, and I don't know that there need to be, since it's not much of a tourist town. But the Carlstadt has a good location, not far from the bus station, near old town and generally in the middle of any action that might be happening.
Our room was not luxurious, but it was very comfortable and the breakfast in the morning was ample. The staff was friendly (especially by Croatian standards) and helpful. At $100 for a double, we found this very reasonable.
I know there were several staircases and I don't remember if there was an elevator or not so anyone with mobility issues should check before reserving a room. Other than that, I would definitely recommend the Carlstadt.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC