Default + is based on the default texture pack, with a few enhancements:
- sleeker ui buttons - I never liked how the buttons in minecraft look all grainy. I replaced the button texture with a smooth, sleek, gradient. They look especially good on the in game GUI that I created from my server http://compassminecraft.com
- more modern in game overlays (crafting, inventory, etc) - I added hints of blue and made everything that was speckled grey into clean, smooth white. Not plain white, but smooth white with shadows and accents and such
- when breaking a block, a status bar tells you how damaged the block is. - I always hated when I tried to break blocks like obsidian and I had no concept of how much longer it would take to break. Now, there is a little red loading bar that tells you in increments of 10% broken
Overall, the interface looks much more modern and simplistic, while the blocks (in there normal, inactive state) remain untouched until you start to break them.