I was on this same cruise, and shared some of the same frustrations, and some slightly different. Random observations below:
Weather was as expected for April in the middle of the Atlantic (I guess I didn't expect warm)
My embarkation wasn't that long - however, if we had arrived to the port even 15-30 minutes later the time to get checked in and aboard would likely have increased significantly based on the size of the lines behind us.
Despite all of the negative reviews I've seen of the 'odd' cabin/bathroom layout that wasn't an issue for us.
The ship was extremely crowded, and to me, lacks adequate public space and completely lacks adequate staffing in bars. I don't cruise as often as many on here, but I've never been on another ship where it was nearly impossible to find a seat, much less find a seat and then have a server notice you and offer a drink. Not faulting the staff - they couldn't possibly have served the number of people waiting in any timely manner. Perhaps weather drove people indoors that might be at the pool in warm weather, but mostly my observation applies to evenings.
Shakers/Maltings are butted right up against each other, and at night it seemed like there was another dueling music show between the band in Maltings and the piano guy in Shakers. The best place to sit at/near a bar that we found was the bar between Cagney's and Moderno. The husband/wife bartending duo there was great! Best drinks on the ship too.
I haven't been able to find original deck plans, but can't help but wonder if the refurb to the ship that 'enhanced' the Haven stole much needed public space from the rest of the ship.
La Cucina is in an odd place reached through the buffet? Not much ambience there.
Mostly the food was very good. Really the exception was the complimentary Chinese restaurant. Food was a combination of hot (what was touching the hot plate) and cold (what wasn't touching the plate), and lacked sauce and flavor. Overall, all 6 of us thought it was terrible.
There was very little space to play games - we mostly had to camp at a table in the buffet (along with lots of other people who also seemed to find this was the only place with a table and where you could hear each other)
Yes, it was disappointing to miss Gibralter, but it happens. It might have been better for the captain to let us know it was a possibility before that morning to set expectations.
I don't think its fair to paint all NCL or other cruise line's ships with the same brush - The Epic just wasn't a great layout for the number of passengers it hold, for this type of an itinerary. I wouldn't sail on it again, but have no regrets for the price we paid.