Starting with the best- you don't really expect characters and dialogue in a tower defense game. I like characters and dialogue- I think they add a lot to atmosphere and player motivation. The gameplay was fun. Maybe a bit on the easy side (I got hit only once), but since this is a jam game, making it easier makes sense. For such a short jam, you added more enemy types, upgrades and uhhh... towers than I would expect! That's also great.
I liked how you went with NES-style pixel art. It has it's charm, and I all the elements were instantly readable. The last boss was a bit of disappointment. After a bunch of animal-based enemies I expected a bear, tiger or a lion. The rest looked nicely though.
The sound was good over all, but towards the end it just stopped and I lost all the sound from the game (I don't know if that was a problem with the game or my PC, but I had sound from other tabs, when I checked).
The use of theme was ok, but I guess I wouldn't know the monsters were "guests" if I didn't know the theme of this jam.
In the end- I really enjoyed the gameplay and the atmosphere, but I think you could have gone harder on the theme! Good job nonetheless!