My husband and I spent 3 nights at the Schlossberg, early December 2011, during an Advent trip we took to Austria. While we certainly got one of the not-so-good rooms, we did, however, enjoy our stay. The location, the staff, and the gorgeous breakfast area made up for whatever accommodation inconveniences we had to deal with.
To start on a negative note (but get over it quickly), we were checked into a dark room, which faced two inner courtyards (one of them pretty picturesque, though). I particularly disliked the very tired (and common) carpet and the office-like bedside cabinet, the sole purpose of which was to host the minibar, meanwhile creating an unpleasant contrast with the rest of the furniture. For an art hotel, I would expect attention to be paid to every little detail. Other than that, the room was spotless. To be fair, however, I should mention that we were also traveling with my parents, and they got a very nice room on the hotel front.
As already pointed out in other reviews, it is the exceptional staff that makes the difference (be it at the reception desk, or in the breakfast area): great welcome upon our arrival at the hotel (friendly, yet efficient), excellent restaurant recommendations, very helpful tips on touring the city, great breakfast service. I also appreciated the fact that the reception staff asked for feedback on the restaurants we had dined in following their advice.
Needless to say, the location is unbeatable. No other hotel I passed by in the center of Graz is better positioned (or looks better) than the Schlossberg. Furthermore, the hotel terrace (which the staff fortunately suggested we visit) is much more than a simple terrace - it consists of several vertically successive small terraces, spreading on the face of the tiny yet unexpectedly rocky Schlossberg hill, each with its own distinctive feature (a romantic sitting place, a swimming pool, a spectacular viewpoint structure). Beautiful!
I also loved the winter garden resembling breakfast area. As for the food itself, it was very good, however a bit of diversity (from one morning to the other) would not have hurt. Also, for this type of accommodation, I would have expected the orange juice to be freshly squeezed.
All in all, it was a very pleasant stay, and I doubt we could have had a better time in another hotel in Graz.