I gave this game two shots to impress me but I just don't see the appeal. First I played it with the keyboard online with a stranger and then the next day I tried it solo with a controller, both sessions were about 45 minutes. I came away from both bored.
At its core Monaco is a pretty basic stealth game with a silly tone to it. There's a little bit of story before each level but it doesn't take itself seriously nor should you. I didn't see anything worth caring about. The majority of players probably skip it altogether. The guards you'll spend your time avoiding also have a bumbling way of acting that adds to the droll atmosphere.
I did like how each character you choose to play as has a unique special ability that enhances their gameplay in some way. I even enjoyed a few chases at times when I did get caught. However, with most chases I never felt like I was in much danger. I have read that many multiplayer rounds devolve into free-for-all sprints through the level with no regard to stealth and I can see why. There's really only two things to do in each level: collect coins and reach the exit. As far as I can tell coins only add to your score on an online leaderboard which I'm probably not alone in not caring about.
Without an interesting story, likable characters, deep gameplay or enjoyable goals to strive for I couldn't find enough to keep me playing Monaco.