If Disgaea: Hour of Darkness was a person, they would have a red hand stamp labelled "Insane" and would be locked up in an asylum cell. Disgaea is some sort of hybrid offspring between Final Fantasy Tactics and someone who has looked at one too many Experience Point scrolls. Your first introduction to the unconventional world of Disgaea is when the main character is (finally) woken up after a two-year snooze by his Vassal, who has tried everything (including a chaingun, blades and a morning star) to wake him up.
The madness doesn't stop there however. Look outside of the castle where you start, at the creatures guarding your fort. Notice anything strange? Notice how, unlike traditional tactical RPG's which cap the level your characters can reach to 99 and cap your Health Points to 999 or 9999, Disgaea's level limit is 9999. Which will probably place your eventual HP somewhere in the hundreds of thousands. And considering the player starts at Level 1, you've got a long way to go.
The game starts off slowly, beginning with a tutorial in basic unit control. The controls are very simple, and before executing moves, you can change the movements of your characters as many times as you want. You can lift and throw characters or stacks of characters to travel long distances across the isometric battlefields, get your characters in the right formation for combo and team attacks, and learn a long list of special attacks, which usually have quite odd execution requirements, like having the 5th square behind you clear so you can backflip onto it. Throughout, objects known as "Geo Panels" will also appear to confuse you, but they can be cleared, if you know how to solve simple colour puzzles.
However, after some relatively easy fights, (the game is handled on a mission basis), the difficulty does crank up a little, and you're given the choice of repeating missions in order to train up your lower level characters. Once you've defeated some enemies and obtained some Mana, you can call the Dark Assembly, which allows you to create new characters from level 1, beg to the Senators for extra Hell (The Netherworld currency) or ask them to change the stock in the shop inside your castle. If they reject, you could always "Persuade" them by bribing them with expensive gifts, or just killing them and passing the motion by "default".
After you return from your missions, you are not automatically healed, so you must go and visit the Netherworld hospital, who for the right amount of Hell, patch your wounds up, only to be encouraged by the nurse there to get beaten up more as they award prizes for the HP you lose. Disgaea does have a storyline, which revolves around three worlds (Celestia, the Human World and the Netherworld, sound familiar?) and demons conspiring with angels and the like, which leads to a rather inexperienced angel being sent to assassinate you, hilarity ensures. The game does have a sly (and sometimes violent) humor streak, which usually involves at least one Prinny (Penguin-like things) getting shot, stabbed or being used as organic hand grenades.
As well as the battlefields of the Netherworld that you fight on, the items that you carry in your pack also have their own little tiny worlds, where many other things live, and by using a service available to you in your castle, you can enter the "Item World" to subvert it's residents so they can be used to upgrade the item they reside in, or be moved into that rusty sword of yours to give it more power. Every level descended inside the item (Some rare items have 100 levels) increases its level by one. This means that even that bog standard spear bought for very little at the weapons shop can be upgraded into a fully fledged weapon of mass destruction.