First of all I would recommend TINA as a free Spice program. The original Spice program was text based, so you had to enter the design as a text netlist and your output waveforms were text files. Modern versions include schematic entry and waveform graphing utilities.

One particular gripe that Bob Pease has with Spice is the global net 0, which is a kind of universal ground. Some opamp macromodels use net 0, but real devices don't have a ground pin. This will give misleading results when a device is operated away from ground.