A shame you could not enjoy the game as much as you'd like to, but your criticisms of it are wrong because I don't agree with all of them.
I'm curious where this game ranks for you compared to the other LM games. So far I'm enjoying it but I'm pretty sure LM2 will be my favorite still.
The three games don't rank far apart, but where exactly I'll put LM3 is still up in the air because I have to spend more time on the multiplayer to see if it's salvageable.
LM1 is the shortest one and without multiplayer, but the gameplay formula was still new. The combat had depth to it despite its simplicity and the mansion was fun to explore.
LM2's mission structure in story mode isn't as good as what the other two games offer, but the five mansions were varied. The multiplayer had some annoying glitches, but it was free to play online.
I don't mind that scarescrapers have been made shorter in LM3, especially that infinite floors got scrapped. If scarescrapers turn out to be beatable without too much stress, then I'll upgrade the score to 7/10 which is the same as I'd give the other two games. LM has been quite a consistent series in terms of quality, each game coming with its own pros and cons. The order in singleplayer is 1 > 3 > 2, for multiplayer it's 2 > 3 > 1 where the ranking can't be anything else for the first game.