The novelty value of staying at the Queen Mary is nice, and the interior decorations and finishings are quite nice; lot's of history here. We did very much like the Observation Bar!
But, apart from that novelty aspect, the rooms are small, no temperature control, the bathrooms small, and (at least in our room) hardly any water pressure in the shower.
It's the kind of place that's fun to stay at once, but I don't think I would stay there again.