some of the 'todo' listing from the wiki, most of which is supported by posts on the forums:
Keyboard layout
- Choose between QWERTY and AZERTY in options or have possibility to choose keys
Remember game options
- shadows configFirst: ClientConfig.xml in windows forms game starter.
Night
- Make daylight gradually darker in the evening. Changing daylight value means redrawing all chunks
Rotate block top face uv for seamless stone texture
Better Renderers\ParticleEffectBlockBreak. Particles billboards
Infinite map height
- Increase play area and mapping options.
Optimization
- Optimize game to run on pentium 3 600 mhz, matrox g200 agp (worse than voodo 2), 224MB