First of all, thank you for checking out this mod in the first place. As the first mod project I have undertaken for Halo CE, it means a lot that someone like yourself thought it looked interesting. Anyways, on to the details...

READ THIS: INSTALLATION!!!
PLACE THE MAP FILE (s) IN Halo The Master Chief Collection\halo1\maps AND LAUNCH THE GAME WITHOUT ANTICHEAT ENABLED!!!

HALO INFINITE EVOLVED: OVERVIEW
Halo Infinite Evolved is a campaign mod for Halo Combat Evolved that borrows some ideas from Halo Infinite and the highly popular mod Combat Revolved, as well as introducing many of it's own original ideas to the mix. The mod includes new encounters, weapons, vehicles, scenery, environments, and a balance overhaul to boot.

ENCOUNTERS
Halo Infinite Evolved includes new and modified encounters in every level, as well as new weapon and item placements. These encounters range from having ghosts and banshee fights in the Silent Cartographer, to world building encounters such as Spec-Ops covenant appearing near important locations (The cartographer, near the bridge in POA, and defending the control room itself. 

WEAPONS
In order to defeat the Covenant, the Master Chief's arsenal has been upgraded with a few new toys.
This includes multiplayer favorites such as the Fuel Rod gun and Flamethrower, but also some weapons that are brand new to Halo CE, such as:
The hyper lethal Gauss Sniper capable of killing anything short of a Covenant Wraith in one shot.
and the Battle Rifle from the Halo 2 E3 demo, which functions like a DMR in this mod. 
All weapons except for the flamethrower are equipped with a Halo Infinite-like Smart Scope which can be zoomed in at will.

Halo Infinite Evolved also changes many of the existing weapons to fit new roles or increase their usefulness on the battlefield:
The Assault Rifle has been buffed to replace the role of the mighty CE magnum with higher damage and accuracy.
The Pistol has been changed to act as a weaker, automatic pistol.
The Shotgun has been given a much slower fire rate, spread, and ammo capacity in exchange for extreme damage, accuracy, and the ability to stun.
The Sniper Rifle is the only weapon not to receive a single change in terms of balancing, but it has received a new texture.
The Plasma Pistol's alt fire has been replaced with a fuel rod shot which takes 50% charge to use.
The Needler is much more accurate and it's tracking is extremely strong.
The Plasma Rifle now functions like the Storm Rifle from Halo 4 and 5.
The Rocket Launcher has a tracking effect once the player gets red reticle. (This also applies to enemies that use it.)
Frag Grenades have been given tracer effects like in Halo Infinite.

VEHICLES
Likewise, the Chief has access to new and familiar vehicles, with the Rocket Warthog, Gauss Warthog, and the Wraith being pilotable in this mod. The scorpion tank, ghosts, and banshees have also received a significant buff with fasters speeds, fire rates and damage.

SCENERY
New scenery also dots the levels to add new environmental storytelling inspired by the novelization of Halo and other later entries. Biomass has been added to some levels in the second half of the game courtesy of the Combat Revolved team. Some scenery may include jumping puzzles and other gameplay alterations.

ENVIRONMENTS
Certain environments have been overhauled: Halo begins in a rainy early morning, and the clouds fade out to reveal a sunrise. Truth and Reconciliation takes place at daytime. And The Silent Cartographer takes place at sunset. Some levels also have less tedium such as Assault on The Control room having 3 of the repeating rooms cut out and replaced with alternate means of reaching the players destination. Certain locked/and or empty rooms in the original game may now also supply the player with weapons, ammo, health, and powerups, so get hunting.

SOUND
The scorpion tank has been given a beefy upgrade to it's firing sound.
Several music tracks have been added/replaced with tracks from Halo CEA, Halo 2, Halo 2A, and Halo 3.
Covenant dialogue is now spoken in English like the later Halo titles.

ALLIES
The marines have been upgraded to take zero damage from the player or themselves. (No more player caused "accidents")
Marines also appear in greater numbers.
ODST's join the fight and are usually found equipped with Battle Rifles.
Marines and ODST's do not suddenly disappear after 343 Guilty Spark and may offer some armaments that may be of use to the player.

ENEMIES
The Covenant horde has also seen an upgrade:
Hunters no longer die to one shot from a pistol and will ruin your day if they get a melee hit on you. (Almost instant death on Heroic and guaranteed death on legendary.)
The Covenant overall appear in greater numbers and fire their weapons faster.

DIFFICULTY
Difficulty settings include:

Game Journalist (Easy):
-Player is semi-invincible (falls and self damage still apply).
-AI companions are invincible.
-All enemies are tuned to their legendary counterparts.
-Vehicles are invincible while the player occupies them.

The way you're actually supposed to play the mod (Normal):
-Player cannot damage allies (carries over to Heroic & Legendary).
-The player can take a moderate amount of damage before dying.
-Enemies are tuned to Heroic settings.

Hard Mode (Heroic):
-Player can take much less punishment before dying.
-Enemies are tuned to Legendary settings.

CBT Mode only for true masochists (Legendary)
-The Master Chief can take about as much damage as a wet piece of toilet paper before dying.
-Enemies fire their weapons like miniguns.
-Vehicles are made of cardboard to save money.
--Your allies are like your teammates in matchmaking, they "quit immediately".