To be completely concise...
FFI: Fight and get exp.  Stats based on class.  All items and spells are purchased. No AP.
FFIIj: Fight to increase stats.  Most items and spells purchased, except pre-determined characters. No AP.
FFIIIj: Fight and get exp.  Most items and spells are purchased.  Stats based on job class system.  AP used for job-change.  Invisible AP for job mastery, based on battles fought, survived, and class.  Everyone KNOWS this is the best.
FFIV: Fight and get exp.  Pre-determined levels for stats and spells.
FFV: Fight and get exp.  Stats based on job class system.  AP used for Job mastery.
FFVI: Fight and get exp.  Magic pre-determined for levels with Terra and Celes.  All other magic learned by Esper.  AP used for Esper/Magic learnage.
FFVII: Fight and get exp.  Magic usage based on Materia, all stats are static per level except HP growth.  AP used for Materia.
FFVIII: Fight and get exp.  Junction/Draw system for magic.
FFIX: Fight and get exp.  Stats are static over all levels.  AP used for support and other magic abilities.
FFX: Fight and get AP.  Stats are static until Sphere level 45/extra spheres.  Magic based on level, non-static.  No EXP.
FFXI: I assume... fight and get exp.  AP used for learning stuff.