LiefLayer: Try FF3 if you want to focus on the gameplay (the job system in this game is pure art).
1 and 2 are not so good 3.
4 is good, but is like a "one class only" FF3 with a story.
5 is a mix between 3 and 4.
I wouldn't really agree with much of this.
FF5 has one thing that FF3 does not: The ability to borrow an ability from another job. In FF3, a Knight who used to be a White Mage has nothing to show from their time as a WM. In FF5, however, said Knight can choose to equip White Magic as a secondary ability, and cast white magic spells like a WM could. (FF3 remake Knight does get some white magic, but only first level, while this FF5 example could potentially use all WM spells if the character earned enough ABP as a WM.)
Also, FF3 does have some significant issues:
* Random encounters don't have enough variation in any given area. Basically, you will use the same strategy in every random encounter in any given dungeon. FF5 is far better in this respect (even Final Fantasy Mystic Quest handles this better).
* The final dungeon is extremely long with no place to save, to the point where it's not feasible to complete the original version without save states or leaving the console on. (Remake versions often have quit save features or similar, except for PSP where I believe the console can be put into hibernation.)
* Bosses are outright immune to effects other than damage. In the original, this even extended to effects like Drain, which would fail if cast on an enemy during a boss fight. (There's an explicit boss flag in FF3.) Compare this to FF5 where status ailments do sometimes work on bosses.
* Attack magic is too weak in much of FF3 (in the remake, attack magic is good early but not later; in the original attack magic is not good until you get the more puwerful summon effects).
* In the original, Bard is useless; in the remake, Bard is useful, but status ailment spells are useless (except *maybe* Sleep, but only because Black Mages get so many casts of it).
* Some jobs have major equipment droughts, making certain jobs unusable for parts of the game (though the remake addressed this somewhat). In the original, Dark Knight is useless until Falgabard, for example. Even in the remake, Evoker is completely useless when first obtained; you have to beat 2 dungeons before you can buy your first summons.
As for other games:
* FF1 may not have as much variety in player abilities, but enemy encounters are much more varied, which keeps things significantly more interesting. Plus, bosses are highly resistant to status ailments instead of outright immune (except for that one undead boss).
* FF2 had some really interesting ideas, which I feel should have been used in more RPGs (though perhaps tweaked significantly). As I said, this game could basically be treated as SaGa 0.
* FF4 is notable in that the game dictates your party composition rather than the other way around. I see FF9 as being similar to FF4 in this regard (except that FF9 lets you choose your party later on, except that Zidane usually has to be in the party).
LiefLayer: 9 is fantasy 7 with worst gameplay (you cannot control the limit).
I see FF9 as a modernized FF4, albeit with its own issues (including what I consider the worst ATB implementation along with FF6 (excluding FF4 WSC/GBA which was outright bugged), mainly due to time not stopping during animations).