TOTALLY agree about check in. We recently were on Carnival Mardi Gras and I COULD NOT BELEIVE how well they did getting people on in an expedited way. The online check in process with credit cards, kids registrations, pre-purchased internet plans we got, passport stuff, was all so easy. MSC needs to send all of their people over to the Carnival check in desk to witness a well oiled machine and make changes accordingly.
Check out was bad however on the Mardi Gras and they didn't advocate people checking luggage and instead brining it off themselves which created a fiasco. On the Mardi Gras you had to go get your departing luggage stickers from the main desk and not from your room attendant like MSC does, assuming they still do that for people not wanting to wheel all of their luggage off themselves. I kind of felt they might be trying to free up labor by getting people to take their own bags off.
On MSC, we usually stay on and eat a long breakfast at the buffet with a few cups of coffee and try to avoid the crowds and just leave later.
For Muster on Carnival we just had to report to our station at our leisure the first day and they scanned our cards and we were done! Viola! Easy Peasy!