Lag fixes. That must be TOP priority. Sort through the code and optimise it further for new graphics drivers. It's now laggy whatever the age of the driver. And fish mobs. And a new world. Make it out of... umm... Diamond ore! That's pretty hard to get! And add furniture. And (pleease add this) Redstone conductor blocks (which transfer current in any direction, possibly just pure Redstone) and make Redstone air-placeable like tripwires. Oh, and glue so that you can make entire walls move with one sticky piston. Basically: 1.5 should be called the electrician's update.
Eh, suppose so. I was thinking of the default, simply because the textures are distinct (plus, since my pack will be pretty simple, I know I'm not stealing from oCd.