There are three more-than-a-decade-old games that I play to this day. This is one of them.
Probably what constantly makes me come back for more is the sheer size of things in the game. You have way over 50 classes, a massive amount of special characters (unique sprites included), a branching storyline and a satisfying amount of little secrets and side quests. The most amazing feature in the game, though, is that you effortlessly micro-manage something around 70 characters in your army, each with individual stats, equipment, name, gender, alignment and abilities. The presentation of the game is so well-thought that you are never overwhelmed by the amount of info thrown at you - actually, you can finish the game without ever noticing a good deal of the numbers, even if only because of the low difficulty. As a matter of fact, the numbers which are going to give you some trouble are the hidden ones: the reputation of the original Ogre Battle (which is now called "Chaos Frame"), which ultimately defines the ending you get and whether or not some special characters will join you.
The special characters all have unique personality traits and the fact that every single soldier you command has a face and a name really makes you feel attached to some of them. The story is big, relatively intricate, and really immersive: on my first play through I found myself ignoring a good deal of side quests to find out what was going to happen.
As much as graphics go, Ogre Battle 64 is quite unimpressive. The artistic job is undeniably good, and its distinctive style is successful in creating a unique visual identity. But the limitations of the pre-rendered graphics are there, and the limited amount of different sprites for each character are pushed to the limit. Maybe a CD would yield better results.
The sound is above average. The music scores are rather good, and there's nothing really bad about the sound effects. There aren't many different music scores, though, so the soundtrack tends to repeat a lot. On the game's defense, the quality of the tunes is enough to make up for it, and I've never felt the urge for muting the TV and setting up another music on my radio system.
The game is quite long: my first play through took me some 50-something hours to finish, while the second (with all the possible side quests accomplished) took me almost 80. Despite of that, Ogre Battle 64 really encourages you to finish it again, with its 3 different endings and various excluding choices (you can't get everything in a single play through). In fact, for getting every single event you need to finish the game at least 3 times.
At last, I apologize in advance for any grammar errors, as I'm not a native English speaker (I'm Brazilian).