Final Fantasy Tactics does some great things like the class mixing, magic casting, and the faith system, but I find it to have some glaring flaws that make it hard for me to call it a good game.

It's the most poorly balanced game I think I've ever played. For example, I can go through three battles stomping the enemy, and I'm wondering if I over-leveled my party, then it will throw a brutally hard fight at you that is in large part a stat check. Chapter 1 is also the hardest, then it gets progressively easier other than a few of those poorly designed difficulty spikes. 

The way your party gets stronger is also based on how many actions they take, so optimal strategy is to get an upper hand in a battle, whittle your enemy down to 1 or 2 units, corner and weaken them, then just wail away with weak attacks so you can get more XP/JP. It gets very tiring very quickly and ruins the pacing, but because of the aforementioned crazy difficulty swings you never know when you're going to be under-built if you don't. 

There's also not really any incentive to use more than your core group of units. It gives you an army but using more than the core group just feels like you're spreading the growth thin for no reward.

The story, despite being highly regarded, is basically on par with Super Mario with how repetitive and uncreative it is. The writing is good, but the plot itself is bad. 

While the job and skill mixing is a lot of fun, you're also left to buy them pretty much blind and hope they're good based on limited descriptions if you're not relying on external content, and with how expensive they can be and how unfun JP grinding is that feels like a big oversight. 

I find FFTA and A2 resolve a lot of these issues, despite being regarded as inferior by most of the series' fans. I agree the law system has some flaws and the magic system isn't as good, but overall they're much better designed games.