Yup, pretty much. The traditional engine nozzle can only be optimized for maximum thrust at one altitude, while the aerospike maintains thrust efficiency at many altitudes, using as much as 30% less fuel at lower altitudes. Also, for the aerospike design, it doesn't have to be a series of small nozzles. The combustion gases can escape the combustion chamber via a ring. It's more difficult to cool this type of system and adds some weight, but it is an efficient alternative to the traditional engine nozzle for SSTO (single-stage-to-orbit) vehicles.
IIRC, the VentureStar was going to use a linear aerospike. With at least one combustion chamber on each side, it seems an easier design than a ring.
Their design seem to indicate they may want to pump air through the spike body to either cool it or as to use it as "bypass" volume in an inverted turbofan-like design. It's intriguing.
