While I know a lot of people prefer the original FF Tactics to the GBA/DS spin-offs (I am one of those people as well), I am still really enjoying this game. I've completed 252 missions, gotten one of the secret characters, mastered the majority of the jobs, and gotten all but 4 of the Scions.
My mine gripe is that the game takes way too long to play through a battle. I'm decently efficient in my quests, completing most of them in 10-15 minutes or less, but the fact that I can't speed up the character movements or turn off the enemy's movement animation all together is dissappointing. Because of the wait, I am almost always doing something while playing this game (watching TV, lurking on CAG, etc.) while I'm waiting for the AI to complete its turn, which has caused some delay when playing and clocked my playing time at 150 hrs. so far.
I shutter to think what my total play time will be after I finish all 400 missions. Also, for those that haven't started playing this yet, I think the Hard mode is the way to go for your first/only playthrough. I chose Hard when I started my file and haven't found a mission that really challenged me yet.