Our first cruise just 4 yrs ago was on the Imagination and we loved the ship. Yes, it is an older and smaller ship, but even on the newer bigger ones, it's impossible to really swim in the polls. They are great for getting cooled off and having fun, though. No ship could have a pool big enough for that many passengers to use.
Also, please remember that there are about 2000 people being served so the food is bound to be similar to banquet food, not a 5 star restaurant quality. We'd sure be paying a lot more for our cruises to get that quality of meals!
Smaller ships have fewer arcade games because there are typically fewer people playing the games - makes sense, right?
As for the smell well unfortunately there are cruise guests who have flushed things down the toilets which clog the system and that will produce the smell. Hopefully it didn't happen for the entire cruise.
Beside these few disappointing things, I hope you were able to enjoy the relaxing time on board, the shows, and other activities going on during the day and evening, as well as the ports you visited.