I would recommend the entire Riddle School series for those who like puzzles, and Riddle Transfer 1 as well. Sadly, Riddle Transfer was supposed to be a 5 game series and jonbro kinda snapped out of the whole "Riddle" project and cancelled with 2 and 3 in development.
Order would be RS 1 thru 5. 4 is an April Fools joke, but it's important to the story. And after that, Riddle Transfer.