Let's start with the good. Presentation was on point. Your graphics style is very distinct, an really brings out the "party" element of the game. The music fit the game, and the sound effects were on point. Have you noticed many jam games have like, two sound effects? Not this one :)
The use of theme was literal, but it worked really well. Although if the theme was not "UNINVITED guest" I'd say all the guests were invited, but one was sort of an a$$hole :)
Here's where I had problems. I tried to play the game three times. First two I got stuck on minigames. In conversation I didn't know what to do (my speech bubbles disappeared), and in the sink and cup game I didn't know what to do. The concept was brilliant- I loved the minigames when they worked, but when they didn't, they derailed the game completely.
Last game I played, I caught the saboteur super fast. Sang karaoke, someone messed with the music, and bam- I got him. Maybe if you had to catch the guy more than once, with him changing the disguise every time? Sorta like a reverse Hitman game :D
Over all- this would be a great game if the gameplay was on the level of presentation. I believe with more time to polish (maybe some more playtesting, or at least hints for the minigames) it would hit that level.