I read Jordan Kronick's Urza's Guilt Deck and decided to make a similar deck of my own. Here is what my deck is composed of:

Land
10x Swamp
10x Island

Creatures
4x Fog Bank
4x Wall of Tears
4x Will-O'-The-Wisp
4x Hypnotic Specter
4x Cephalid Broker
4x Lore Broker

Spells
4x Megrim
4x Urza's Guilt
4x Recoil
4x Duress

In Jordan's article, it appears that the Abyssal Nocturnus is his main offense with just a couple of Urza's Guilt thrown in to finish the game. He mentions that the problem with most Megrim/Urza's Guilt deck is that it lacks defense but it his deck still seems to lack defense.

I threw out Abyssal Nocturns entirely and decided to make this deck a little more defensive minded. So, I put in Fog Bank, Wall of Tears, and Will-O'-the-Wisp to control the pace of the game.

How competitive is this deck in your opinion, and am I just throwing in too many walls?

Let me address the second question first.  Will-o'-the-Wisp I actually like a great deal-- it's very cheap to cast, and with regeneration it's very hard to kill.  It can hold off just about anything as long as you keep a Swamp open.  However, 12 walls is too many for any deck that doesn't use Rolling Stones or Wakestone Gargoyle.  Drop Wall of Tears and Fog Bank.  I am, however, going to give you some other walls to put in their place: Drift of Phantasms.  Why Drift?  Because they have Transmute, allowing you to search your deck for a 3-mana card.  And since some of your most powerful spells--Megrim, Hypnotic Specter, and Recoil--are all legal targets for Drift to search for, then I assume you'll want to Transmute more often then you'll want to play the 0/5.  So, in go 4 Drift of Phantasms.