It's been over a week, and it doesn't feel like I've made too much progress, so I'm going to bullet-point everything I've done and I bet it'll be loads! First of all, I overhauled the game's art based on feedback from other Playdate developers:

• Went back over all art assets and adjusted them for better clarity and contrast
• Experimented with different dithering algorithms and re-tooled pipeline so that I can switch between Atkinson, Burke, Pigeon and Floyd-S. Overall, I think I'm sticking to Atkinson as it's the least noisy, has greater contrast, and looks better in motion/during transitions.
• Added outlining to player-wielded items to help them stand out from the background where the item's edges aren't already all-white or all-black

Here's a side-by-side of the overhaul vs the old art - from the same area of the game if not a direct comparison:

As well as working on the art, I've also made an animated system launch card plus nice fade in to game:

Added food and drink. Various foods give different levels of health over time, and the beer gives a 30 second 75% incoming damage reduction (liquid courage!):

I've also begun work on audio, including stereo positioning (for use with headphones) and volume rolloff for distant events. 

With work on the first dungeon pretty much complete - and that includes a lot of mechanics that will be used throughout the game - I now have a plan for the remaining four areas of the first chapter (and initial release) of Etad.