The area effect is confusing I agree. What it says is:
Effect anchored plane of ice, up to one 10-ft. square/level, or hemisphere of ice with a radius of up to 3 ft. + 1 ft./level
Then:
Ice Plane: A sheet of strong, hard ice appears. The wall is 1 inch thick per caster level. It covers up to a 10-foot-square area per caster level (so a 10th-level wizard can create a wall of ice 100 feet long and 10 feet high, a wall 50 feet long and 20 feet high, or any other combination of length and height that does not exceed 1,000 square feet). The plane can be oriented in any fashion as long as it is anchored. A vertical wall need only be anchored on the floor, while a horizontal or slanting wall must be anchored on two opposite sides.Each 10-foot square of wall has 3 hit points per inch of thickness. Creatures can hit the wall automatically. A section of wall whose hit points drop to 0 is breached. If a creature tries to break through the wall with a single attack, the DC for the Strength check is 15 + caster level.
So you cannot make a block of ice it has to be a plane or sheet, or make it thicker than 1" per caster level. So an 8th level caster will create a wall of ice 8" thick and consisting of eight 10x10 planes in total area.
It's a great spell for blocking off foes on one flank for a few rounds so that you can concentrate on the other, or for making a fire attack stop dead. It can make a temporary bridge, or chute, in fact it's a very versatile spell in many ways.
Don't use it to trap them all at the same time. Split the group with it and let the now isolated members of the party sweat it out.