Source ports have allowed authors to craft magnificent new worlds confined only to their creativity (and moving sectors).  Action Doom, Doom: Carnage League, Super Sonic Doom... all drastically change the game mechanics to create a completely different game.  While fun in their own right, they cease to be Doom, leading many purists to cry 'foul' and ask where all the good "Doom" levels have gone. 

Simplicity bridges the gap between enhanced levels with the aid of modern engines, and the simple gameplay that made Doom so addicting.  The title, Simplicity, comes nowhere close to describing Agent Spork's masterpiece, as these levels are anything BUT simple.  Simplicity's architecture is phenomenal, and has that special touch that lets you know it's a SporkMap(tm).  Transparency is used to gorgeous results, slopes are used but integrated as to feel natural, and several new monsters make Simplicity feel like an official Doom addon. 

Too often when a wad has "Requires ZDoom" I brace myself for particle fountains and ugly on screen messages from <Sarge>, but AgentSpork has managed to seamlessly integrate the power of ZDoom with the "simplicity" of the underlying Doom engine.  Coupled with one of the most creative secret levels conceived for Doom, Simplicity is easily one of the best.

Scythe 2 - Erik Alm

Scythe was released in 2003 and was crowned one of the years top 10 maps.  Now, two years later, its sequel takes top honors beside it on Doomworld's "year's best" list, and is it any surprise?  If Scythe was that good, it's only reasonable to assume Erik has had plenty of time to hone his mapping skills for the sequel, and boy has he ever.

Personally, I respected Scythe as a megawad, but never enjoyed the look of the maps very much.  All that changed with Scythe 2; the last dozen maps are not only breathtaking for the sake of the wad itself, but all maps that have been made.  Overgrown bases covered in vines and weeds, vast gothic cathedralesque locales, and sinister hellscapes are just a few of my favorite themes.   I lack the qualities required to convey to you through words just how beautiful the last few levels of this megawad are.  Some may be turned off by the Hell Revealed style gameplay towards the end, but remember, monsters can be turned off as well.  Do yourself a favor and play Scythe 2 now, if you haven't already.  And if not, what the hell is wrong with you?

Followup: In 2009, Erik Alm completed the final 3 maps that were missing from this build, and various bug fixes. This only reaffirms Scythe 2 as one of the best projects available for Doom... whether it be 2005 or 2009.

HedRox - Rodrigo Acevedo

With so many major releases, some levels always soom to fall through the cracks, and that would be a shame for HedRox.  This creative level was released earlier this year and lost, swept under the rug if you will, by so many other releases.  Reminiscent of Vrack, this cramped, gorgeous mapset was a treat amidst the plethora of cruddy old maps that flooded the weeks of newstuff this year.  A complaint of the map was the close quarters fights with the obtrusive architecture, but the gameplay is still fun despite this, and it looks very nice as well.