First 3D Castlevania on PS2. Not a bad start....not at all... =)
Leon, as Quincey in the novel, goes in for revenge, since a vampire named Walter (lord of the castle) has kidnapped Leon's beloved. At first Leon can't resque her, since he lacks the power to affect Walter by any means.
He then returns to Rinaldo, the old alchemist who he encountered in the forest earlier, only to reveal that he has lost his loved one to the evil vampire Walter. Rinaldo then offers a whip, the "Vampire Killer" as a weapon to strike Walter down.
As soon as Leon returns, he notices that he can't enter the door where Walter escaped. To open the blocked door, Leon has to fight 5 bosses, in order to break the seal. Each boss is located on a different stage, and you get to choose which stage you want to play through. There is no pre-determined route you have to go. There is however, a few additional bosses you can choose to fight, if you're aiming for a perfected gaming experience; Flame Elemental, Ice Elemental, Thunder Elemental, and at the bottom at the castle, The Forgotten One (He is pretty tough, so, be prepared for a long battle).
Lament of Innocence isn't a hard game. It doesn't even put up a challenge. The only boss that gives you proper challenge is Death, and maybe The Forgotten One.
It takes about 4-5 hours to get through LOI - no trouble to it.
After you beat the game once, you get to try out a few bonuses. Such as the "crazy mode" (much like extreme hard mode), "pumpkin mode" (play as a pumpkin (leon?), "joachim mode" (play as the inprisoned vampire Joachim you fight in the game) and so on..
As the first 3D Castlevania on the PS2, I'd say Konami has done a great job, could have been better on certain things, but still, it's a good first run.