Love the look and feel, but there are a few things about the game that really brought the fun level down. The first is the equip/unequip system. I'd really consider adding the good ol' mouse wheel/number keys for the inventory items so you don't have to go into the menu to heal, take out your bat, etc.
And speaking of bat, the combat felt quite unfriendly. Almost like the player is punished for even considering it. Especially against the yellow guys who kill you in one hit. If nothing else, since you're encouraging stealth, the ability to kill any enemy from behind if you can sneak up on them seems like it'd be a nice feature. You know, when you're in range, have a prompt appear that lets you know you can safely take the bad guy out.
Other than that, not pausing the in-game action while having the menu open felt a little unnecessary. If you're not going to allow the player to quickly scroll through items with the mouse or by using hot keys, I think you should at least give them time to do what they need to do in the menu without fear of being attacked.
Like I said in the beginning, the game is visually pleasing and plays smoothly. I enjoyed it. I just think I would've enjoyed it more if the issues I brought up hadn't been there.
Here's my no-commentary playthrough: