Breakdown by BetaM.
This video released in May 2004 includes footage from a build likely between December 2003 and March 2004 aswell as some Travellers Tales watermarked footage.
General
The HUD is made of text using Crash Nitro Kart's font.
There are many placeholder sounds, some coming from Crash Bandicoot: The Wrath of Cortex, or earlier Crash games.
Crash's spin model has a bigger plain shadow.
Wumpa fruit have no shadows.
Explosions have different, simple particles.
Wumpa suction speed is slower.
The Rollerbrawl has no smoke particles.
There seem to be no gems or gem puzzles.
Humiliskate sometimes has Rollerbrawl particle effects.
There are no music or ambience tracks in the footage.
Crash's idle animation is missing facial animations.
N.Sanity Island
This area, which in the final game is occupied by a few wumpa trees and monkeys, is quite empty.
The farm is at ground level, with a pack of Nitro crates sitting in front of it.
Cortex's attached crystal doesn't disappear after a throw.
Tikimon has an odd spinning animation and does not spawn minions when he's vulnerable.
Cortex seems to have a buggy running animation while attached here.
Tikimon is missing the dirt pile around him.
The object layout in Doc Amok is a bit different than final, missing a nitro detonator and a gem.
The spiky hazard has no destruction animation and just pops out of existance on taking damage.
Cortex's running animation in Doc Amok is the same as his regular one.
No locked camera in the boss arena.
No spikes around the arena ring.
A stack of crates exists here that was removed later on.
More crates that were removed later on.
The spiral is missing timed drop platforms.
The button on the drill is much smaller.
Sword ants appear to be missing.
The area contains many more crates of multiple types.
Iceberg Lab
The area is missing the surrounding sea.
Much of the detail is missing, including trees, rocks, crates and wumpas.
The floating ice platform's texture is much brighter.
The level is missing snow particle effects.
Cortex's switches are consoles that function the same way.
Uka Uka's arena appears to be outdoors (still without the surrounding sea).
There is only one exit from Uka's arena.
Uka's texture is bugged.
The switch platforms have metal support beams connected to the main ring.
Uka's main button is surrounded by a pit that the player jumps over.
Slip Slide Icecapades has many more chunks which are varied more with unused setpieces and structures.
There's a lot more different metal structures embedded into the terrain.
Slip Slide Icecapades' terrain is a lot more glossy.
The level is missing snow particle effects.
The first visible frame shows a metal object in a familiar chunk.
A pipe sticks out on the right side of the picture in the same chunk.
Gone a Bit Coco
This is the only known footage of the level Gone a Bit Coco.
It doesn't show much besides the supposed starting area of the level.
NOTE: This footage contains a Traveller's Tales watermark.