Oh, diagonal movement was actually the only major feature that I thought this game needed :D
Diagonal movement is a staple feature for many RLs, and is actually pretty important from a game design standpoint in my opinion, as it adds a bit more depth/ tacticality to the mechanics. It also makes it more difficult for the player to get away from difficult situations simply by running away (because enemies can move and attack diagonally, it's harder to completely avoid their attacks). Of course you don't need to implement a feature that you are unsure about, these are just my thoughts :)
A different way to make the enemies a bit harder for the player to run away from would be to give some monsters a "dash" ability, which would allow them to move and then attack the player all in one turn, or move two tiles at a time. Some roguelikes use a mechanic like that.
Good luck with the game, I hope it hasn't been abandoned?