FFL battles tend not to be exciting. There are exceptions, of course: Archie is a decent opponent, and Gilgamesh is as hard a boss as you will find. It really feels serious in these fights and that's why they are worth working towards.
The rest of the game is kinda meh. From my PoV, the problem is that huge HP totals are being substituted for effective AI design. The problem is that once you figure out a strategy, all there is left is the long HP slog. The bosses have no "disaster attacks" by which to mix up the gameplay. All the disaster attacks in the original game have been dumbed down to the level of the . The only disaster attacks still of note are Golbez' Meteo (original to this game, granted), and the HP-to-1 moves. Of course I hear that work on the Magus 3's Delta attack is ongoing, and hopefully there will be status effects in the near future. Still I expected to be savaged by Rubicant's Glare tornado, but was disappointed when I wasn't.
Part of the problem I think is that the same AI scheme is being used for both single player and multi-player situations. The single player game can only get so challenging because of the simplicity of 1-to-1 combat. Not a good idea to put much work into it.... In fact, the outcome of the battle can be easily calculated before it even begins. Not so with multi-player, and this is the reason for its appeal. I really enjoy the multi-player game and think a can be done to improve it by making the fights less predictable, and maybe just a tad shorter.
To illustrate the severity of the length problem, consider the fight against Proud Clod in FFVII. Without a doubt the most disappointing fight of the game. No one who makes it to that point ever loses that fight because it's attacks are weak and it's very slow besides. The battle against Proud Clod consists of hacking away at its parts until it's dead, over something like, 15 minutes. Now contrast this fight with the Diamond Weapon battle only a few minutes earlier. While briefer than the Proud Clod battle, it is much more exciting because the monster resists physical attacks (most of the time) and has a beam that reduces HP by 90% with a chance to confuse. Absolute chaos erupts as the player must immediately figure out what has happened, who is confused, how to respond. And while the player is still trying to recover, Diamond Weapon is back on the attack, dealing stomps for 2k damage. The first time you play it completely devastates you and even on subsequent plays it's not easy to recover quickly without adequate preparation.
Final Fantasy is fun because it has thrilling battles which really drive home the hate against the opponent. FFL... not so much.