This is the second time I cruise with MSC along with my family of 4 -- myself, both parents, and sibling. This time we set sail on MSC Seaside, but I'll attempt to compare the experience with my next best knowledge having set sail two years prior on MSC Divina.
In general, both ships are very luxurious, from the evening dinners (especially the gala night) to the overall look and design of each deck. MSC definitely caters to an international audience which is really neat if you want to immerse yourself in different cultures. There were many European guests throughout the ship, and most of the staff throughout the ship are literally from all over the world.
MSC Seaside is a gigantic ship and feels just as such when walking through the different decks. Although, it did seem bigger than MSC Divina, much of the extra space felt that it went to more decks for extra cabins to fit more people on the ship. The decks on MSC Seaside where the fun happens seemed very similar to those as the MSC Divina with the exception that it did seem to have an extra pool throughout the ship and an extra Buffet restaurant, but the main theater did seem smaller compared to the one on MSC Divina although it had 3 different show times each night compared to the two on MSC Divina.
We chose a balcony cabin this second time around as we were spoiled with an upgrade to a balcony our first time cruising with MSC Divina and we really liked it, so their strategy certainly worked out well for them. The only difference is we tried to fit 4 people this time around in one cabin compared to having two cabins before. This did feel somewhat crowded and the room felt smaller despite probably being a bit bigger than our first cruise. Our cabin keeper was great, however and pointed out all the great spots to store our suitcases and was did a great job tiding up after our mess twice every day.