Are you talking about Dark Moon? If so, the game is pretty decent. However, the game is broken down into missions meaning that if you are to complete the main objective for that mission, you are taken back to Professor E. Gadd, ruining the flow of the gameplay. To add it up, you don't have full access to an entire mansion if a mission doesn't intend you to go that way. If you don't mind that all, it's pretty good!
There are gems to collect and hidden boos to find. You have to be observant of the things around you and use all the tools available. If you haven't played Luigi's Mansion 3 yet, it's better than Dark Moon in my opinion.