Click the image for the G/ZDoom version. The Zandronum version can be acquired here.
The primary emphasis in Burl Tumd is speed: EVERYTHING happens faster. You move faster, you kill faster, and you die faster. Weapons are made to be far more responsive and powerful, and in addition to speed there's a large emphasis on efficiency. Playing intelligently and using the right weapon at the right time will let you tear through the hordes at incredible speeds, whereas rushing in blindly will get you massacred quickly. I highly suggest that you read the .txt past the screenshots before playing so that you at least have some idea of what you're doing.
Additional features include:
Spoiler:Several pints of multicolored ketchup, with new weapons to extract it with:
Spoiler:New enemies, as well as modified old ones:
Spoiler:A readme written in similar style to how the name of this mod came about: READ ME (Readable version here.)
All this and more for less than one megabyte!
Please note that this isn't quite feature-complete yet - in particular, the rocket launcher animations are painfully half-assed, I intend on adding a BFG replacement at some point in time and I haven't buffed up most of the enemies yet.
Credits for resources used are included in credits.txt in the root folder of the PK3.