I've been there 5 nights, the Hotel is beautiful, with great amenities, modern with some ancient touch. Staff is very helpful and multilingual, rooms are spacious, clean and bed are really comfortable.
There is a nice bar/lounge area and also a patio garden enjoyable during sunny days.
Only negative point: breakfast. Is not a 4 star breakfast, but has a 4 star price. 20€ per person and poor food choice. I expected more, to be honest.
Other than that, I will come back there for sure!
Great hotel, great the Montparnasse area (everything you might need or want is around the corner), great quality/price ratio.