This 'game' is merely a prologue to a series proper. It's so short it won't wear out its welcome and overall is OK.
Given that the game is less than 10 hours, there's not much depth in any respect. As there's little to the game but positioning your characters and attacking or using spells, Arc will get old fast, but not as quickly as it finishes. You could pursue some of the side-quests or grind levels, but it's not really worth it. The game is extremely easy - so easy that when I beat the game I didn't even realise that I had. I believe it was because the game was too long in development and had to be rushed out the door; either way it doesn't stand alone from Arc the Lad 2 which is a direct continuation of the unresolved plot.
In terms of the story the game is too pastoral and sentimental, almost naive. If you've played any of the legion of Japanese RPGs set in a quasi-European medieval fantasy world you get the idea. Destiny calls, young hero picks up his sword in search of his father, mother expresses reservations. Young super-deformed hero meets girl with equally super-deformed features. It sets up the storyline for later at least. The noirish flair of Arc the Lad II utterly destroys this lesser, but serviceable introduction to the series. Given its length and difficult Arc is recommended for those new to strategy RPGs but it should be swiftly set aside for a great offering like Final Fantasy Tactics.
My recommendation: play it if only to power up some of the characters for Arc the Lad 2, which is far better in every respect.