Overall we had a great time staying in Mariefred - Gripsholm castle was amazing and the town is very charming. The hotel promised a lot and the staff were excellent but overall, it was a let-down. Some things didn't work properly: the light in the hall of our room kept flickering then failed, even after being 'fixed', the drains in the beautiful, slick bathroom smelt really badly (even thought the batroom itself was spotless), the internet was lousy and the very expensive dinner was very bland and not worth anything near the price charged (Chicken roll with soggy 'crispy skin', tarragon powder, a bland gravy and carrot puree is not worth 30+ euros).
The building is beautiful with a lot of the original decor lovingly maintained, but we just couldn't help but be reminded that we were in a corporate hotel, not (as the brand promises) a cultural pearl.
If the room / internet problems were sorted out, the restaurant was to serve food worthy of the price tag and the stacks of products for sale in the lobby made a lot less obvious, then it could have got 5 stars from us but it simply didn't deliver.