This mod adds several new block properties. The most noteable is the tower/dungeon blocks. They range in color and vary in use. The first thing you'll notice is that the housing blocks have no breaking animaton. Only in creative mode you can break the outer edge of a dungeon or tower. The inside chambers/levels have differently colored blocks that behave like normal stone bricks.
The obsidan block can be mined by using a golden pickaxe (cannot in build 6.0). It can also be created by using the bucket trick. Portals to the nether work well and fully(SMP bugs are few and far between).
The block break hierachy is:
Iron<gold (iron, lapis)
Diamond/Dragon's Tooth (redstone, gold, diamond, obsidian - needs confirmation)