I found ngspice extremely useful. I have compared the results with Cadence Virtuoso and the results are usually identical or with negligeble difference. I am trying to use a combination of ngspice and magic for IC design.
Micro-Cap is Windows-only software (it runs on Linux via Wine though) and perhaps more accessible than your current (which probably is "make circuits somewhere, generate netlist, simulate with ngspice, analyze somewhere else") workflow as it has an integrated schematic editor. The most powerful Linux alternative to Micro-Cap et al is probably KiCad.
