In LD22 I used a decent framework (melonjs), but had never used it before and suffered a significant time penalty learning what I could and couldn’t do with it. I spent way to much time tinkering and learning.
In LD23 I built everything from scratch (for a text based game). I knew the tools well, and didn’t need a bunch of art, but I spent most of my time on framework. The story and game-play suffered significantly.
This time around, I’m opting to use tools that I’m familiar with, and that provide a significant amount of framework to build atop — I’ll be using LÖVE, and probably the Hump, anim8, and, possibly, advanced tiled loader libraries.
The downside is that they won’t be immediately playable in the browser, but the upside is that linux, osx, and windows are all supported, and there’s not much to install.