One of the pregen characters for the PHB2 Release Game Day Adventure is an 11th level drow Avenger. She is a divine melee striker that selects a single enemy within 10 as her oath enemy, has all kinds of bonuses against that enemy, and keeps that oath enemy until they are dead, or the end of the encounter.
For example, Censure of Pursuit gives a significant damage bonus if your oath enemy willingly moves away from the avenger.
If you attack your oath enemy in melee and they are the only enemy adjacent to you, you roll twice to hit them, and choose the best roll.
Bond of Pursuit lets you shift towards your enemy if they don't end their turn next to the avenger.
Essentially, Oath of Emnity is something like Hunter's Prey, but easier to select, and with lots of neat doodads instead of straight dice of extra damage. It takes some manuevering to make the best use of it. You can't switch oath enemies until they die, and they will have a hard time avoiding you.
This Saturday will be the PHB2 Release Game Day, and there's probably a store near you hosting the adventure. It's a good chance to test out the characters, but if you haven't played paragon (or the DM hasn't), the characters are fairly complex compared to heroic, with lots of powers, especially reactions, interrupts, and triggered free actions. The Wizards website should have an event locator you can search for a store near you.
Smeelbo