I've sailed on Cunard many times and QM2 is a favorite ship, as is the crossing. An offer that was too good to pass up arrived in my in-box (for a single cabin!!) and I booked this crossing one month before departure.
Embarkation in Brooklyn was very quick for me (on the ship 30 minutes after arriving at the terminal). This is why I was able to get through quickly: I read all the directions in the email communications from Cunard and PRINTED my boarding pass which was the first step to skipping the long line outside; I had my vax card & test results ready; I did the on-line checkin, including uploading a photo & credit card info; and even though the Cunard communications said that Diamond level passengers would not get priority embarkation, I asked if it was available and it was.
The ship was not full (I heard about 1600 pax); attendance at lectures and trivia events was quite good; and everybody seemed to be enjoying the ship (except for the WiFi, which I heard multiple complaints about). As always, a global mix of passengers and many first-timers to Cunard.
So wonderful!! These single cabins on Deck 3 have two huge circular windows (maybe 4 feet in diameter) and a real shower with glass door instead of a shower curtain. Large room, double bed (maybe the size is something else, but it's definitely bigger than a twin bed); comfy chair in front of one window; chest w/mirror, drawer and fridge; credenza under the TV with more storage space; roomy closet w drawers & safe. Bathroom was more deluxe than regular cabins (marble-look counter).