We really enjoyed our stay in Grosseto at the Hotel Bastiani. It's in the heart of the old center, a block from the Duomo. We walked from the train/bus station - an easy 10-15 minute walk, and went on a day-trip to the beach at Follonica, using the train, also. The hotel rooms are large, and the bathroom was nicely furnished with a large bathtub/shower combo. The breakfast area was also very nice with a large assortment of items, and excellent cappacino. Each person at the front desk was very personable.
We planned to use the bikes available but ended up walking everywhere, instead. While we were there, the old center had a wonderful night event with lots of music options, arts, and museums were open.
We know that Grosseto is not the typical location American tourists go in Italy, but we really enjoyed our time there and recommend it.