A good hotel (near a large supermarket) - with all the core essentials for a business traveller. Modern decor (its a new hotel) and friendly staff. They've always given me the quiet room I've asked for. Food is fresh, bed is great, wifi access and modern bathrooms.
Only possible irritations: timing for being able to order dinner is quite limited, the menu doesn't change - and lunch is not always available. Breakfast is adequate but don't expect anything lavish.
Overall, my preferred hotel for Mannheim.