KING-JANS is right.
Other isometric games (Marble Madness, Snake Rattle 'n Roll, Q*Bert, etc...) have right arrow move you down-right, up arrow move you up-right, left arrow move you up-left, and down arrow move you down-left. As if you grabbed your controller and tilted it 45 degrees clockwise, rather than 45 degrees counter-clockwise as this game does.
Good thing you can click on the arrows because with the current control scheme that's about the only way the game is playable for veterans of other isometric games.