It's very rare to find a hotel that ticks ALL of the boxes. Especially 5 star hotels that actually live to their reputation. But let me tell you that Le Grand Mazarin is all of that and more.
The location is perfect (in the middle of La Marais), the room is super cute and sparkly clean, the room service is quick and efficient (they cater to allergies very well), but most importantly, the staff is so kind and helpful. They helped us with any query, no matter how silly it was (and we had some varied questions regarding shopping, art exhibitions, transport and whatnot).
You can see this new hotel is pure quality, the closest in similarity I can think of is the Four Seasons in Hampshire and the Ritz in London (albeit the rooms in Mazarin are smaller, but service is better). All in all - couldn't recommend it more.