While the original focused on making the setting feel like a liveable mansion that got taken over by ghosts, the second game is more about "spooky places". Luigi travels to many different settings, such as a haunted mansion, a greenhouse, an abandoned clock factory, a snowy shack over an icy cave, and more. Sadly, I can't relate to many of these settings. The first game's mansion had a certain "warmth" to it, especially when cleared out of ghosts, and anyone can relate to a house-like setting.
Here, the settings not only lack that, but feel blatantly puzzle-based. In many cases, simply navigating a room often means having to solve puzzles. You might have to use your vacuum to grab onto a pulley and carry yourself from one side of a crevasse to another. Not a problem if you're doing it for the first time, but unfortunately, the rooms that involve solving a puzzle to figure out how to navigate them remain puzzle-based even after the puzzle has been initially solved. This stands in contrast to the first game, where navigating the mansion was more like navigating a mansion in real life, with puzzles stopping you only once. What's more, due to the sheer amount of puzzle-solving required to merely travel, the locations don't have convincing room layouts.
The game's mission-based structure means that you visit the same area multiple times to do different goals, with changes to what's going on. This might sound like a good thing, but the game is just not open in its design. Instead, for the most part each mission restricts you to its own specific puzzles and locations, not giving you the freedom to explore that the first game had.
Where the game fares better, is multiplayer. I actually used to daydream about how multiplayer might work with the first game, picturing multiple different-colored Luigis exploring the mansion freely and independently. Well... that's exactly what we get! The mansion is randomly generated, and the players have incentive to work together, as the game does not scale difficulty. "Fainted" players can be revived, and players can communicate by making Luigi himself talk. It lacks major depth, but it's fun, and I love multiplayer haunted house exploration. Sadly, players cannot join mid-game, so if someone quits, the player count is lowered for good. A major oversight in the era of Drop In Drop Out Multiplayer