Well, it's readable to say the least. My main problem is that you use what I like to call "the Fratboy" tone of voice. A lot of IP's use this style when they add the odd line (or vandalise). This is often reverted. The reason being that it's too opinionated, too blunt, too basic, and too unfunny. Now please don't be offended, because I am in no way saying your writing is as bad as that. I'm just saying that for an encyclopedia article, the voice isn't really that encyclopedic, and jokes would benefit from a more intellectual tone. Sometimes the wording and phrasing of what you're trying to say is reminiscent of a 8-year old recounting a book report eg. "they thought Master Chief was dead, and Sergeant Johnson said take him away, but then Master Chief surprised them and got up. Then they went and killed some aliens, and then they went to another planet, and then they self-destructed the ark, finally winning the fight." I'm sometimes inclined to write this way myself. Just get a thesaurus or use an online one if you're struggling to get the right wording. You'll see what I mean as I go through the rest of the review. And make sure you keep your tense consistent in the middle of a sentence, and please be more careful with grammar.
Thought the covenant really sucked.
Oh, just look at the grammar section...
but when they offer the hunters to join...
Therefore the Covenant threaten to destroy there planet from space, making the Hunters surrendered and joined the Covenant.
When the Grunt didn't like the way they were treated, as they were used as couches for the Brutes and the Jackals keep bullying them, they rebelled.
they were forgiven and their species.
(Which includes you) <insert word AND here> they destroyed the planet Harvest (a human colony).
But the human sent out he Spartan II's (which includes Master Chief), gene(t?)
ric(ally) altered human(s?).
But after the Covenant destroyed Reach, one of the most important military planets in the human race (I didn't realize constellations and large orbiting masses were capable of being included in the human race.)...
manage to escape
which was easy for them to do since they're much more advance and better than us, they land on the the giant ring.
unaware of its true purpose,(perhaps a semi-colon instead) to blow everything up.
After the Master Chief managed to get in one of their ships, they founded Halo's Control Room.
an alien parasite that controls a host while the host is still alive, and (their/who's) main goal is to scourge and take over the galaxy.
Master Chief manage to overact(?) the engines
but (created?) a problem
to (for?) Thel Vadam.
After there floating High Charity found the Halo, they were disappointed when they founded it destroyed.
Then the Covenant founded Earth, which is bad, by the way, and founded another Halo, which is worse.
the Brute(s?) switched with the Elites.
Then the Prophet of Truth found Earth, (while? and began? It's a bit ambigous) looking for the Ark.
The Covenant Loyalist(s?) (which has the Brutes) founded (I finded the repetition of this word a lot.) Earth and the Ark.
There plans were foiled by the Covenant Separatist(s?) (the Elites) who joined the humans, killed every Loyalist, killed Truth, and (the? I dunno, The might be part of his name, so could require a capital) The Arbiter and master Chief manage to destroy the Flood, and the Ark, ending the War
The <insert the word "arbiter" here> is a special role of an Elite in the time of need.
except the one during the Taming of the Hunters, were a Hunter killed him
The most famous one, Thel Vadam, (see below) was the only Arbiter who remains alive (also technically a contradiction in terms depending on how the arbiter system works. I'm a bit fuzzy myself, but if there's only ever one arbiter, then he either gets killed, or lives. It's not really that much of an achievement to be alive at the end of Halo 3 in respect to arbiters. It might be if no other arbiters survived their respective wars. think on it.)
then the Jackal is he right alien for you.
...pistol with a shield gauntlet but with a few easy shots the shield will over heat and turn off then is easy to kill but if you don't take out the shield they can be a real pain in the ass (just read this sentence, please)
They are the main soldiers for the Covenant until they were switch with the Brutes.
have Active Camoflage
They have a very organized class of rank (the colour?) White being the highest(,?) the average solider has standard blue Armour an just above that is red then gold then black then white grunts also have this ranking system. (just rewrite this section into clearer english please. Full stops are recommended)
They love using spike (Are you referring to ammo types? is that the right word?) for their guns rather than plasma like the rest of the Covenant.
A Hunter are not one single being, but are made up of eel-like aliens like a Man-O-War.
...and the spikes on their back can cut through anything. (do you mean the spiker gun can cut them down, or that they have sharp spikes on their back. I don't remember them having spikes or ramming their backs into me when playing Halo 3.)
Although they have impenetrable armor (,?) they have flaws in the armor <insert full stop here> they don't have any armor were what looks like the back and abdominal area <insert full stop here> a few shots there and the big bastards will be dead before they hit the ground.
They are very good fixers at stuff (please reword)
old_people aliens (any reason for "_"?)
Mauler: An rip off version of the shotgun.
Shade: A weapon that shoots out a lot of plasma. They are exremely dangerous.
Gravity Hammer: The Brute<insert apostrophe here>s ultimate weapon. One hit and your K.O. They're only used by Bute Chieftain.
Energy Sword: A weapon that is like a lightsaber, but is more sword like. One hit and your dead. There used by high ranking Elites
This things may be small, but don't be fooled.
But (buy?) in the next 5 minutes it'll cost $250, and we'll send a bonus Ghost and a very cool flashlight, so call now.
They are also very annoying if an enemy is using one, and man people
The noise they make gives you a warning that one is near by (nearby), so you better hide, or very little will remain of you. The best way to destroy Banshees is (to?) use rockets, machine guns, tanks, missiles, (or?) and another Banshee. They are big floating tanks with a shit load of heavy armor and has two powerful weapons
take out enemies in close range, mid range, and far range (you could almost say "any range")
It secondary weapon
It<insert apostrophe here>s like the Ghost but is more dangerous
The beam that shoot(s?) out is extremely powerful
They can not be destroy on the outside,
have a weapon that turns a planet<insert apostrophe here>s surface to glass and use them to make fancy glass cups and stuff.
they carrier the Covenant's equipment
He killed Truth later and help Master Chief destroy the Flood
He survive the war and return home on his planet. He was given the Noble (Nobel) Prize for being the biggest bad ass alien in the universe.
this Arbiter is a complete jackass who cars little for any one
He spared the Thel Vadam's life and offered him to become the Arbiter
Then he gave the Arbiter to retrieve the Index
He then manage to find the Ark
and manage to activate all the Halos
On (at?) his funeral, many people just came to make sure he's dead, while the others put grenade in his coffin.
I suppose for fairly listy subject matter it fits. Might want to keep images to the right if there aren't many.
My hand hurts from typing all those out... Oh, and get yourself an opening paragraph. You need a good introduction giving a general overview on the Covenant.