Why is halo 5 campaign so hated? I never played it, so please tell me, before i decide, if i should buy it or not.
Instead of buying the game you could use Game Pass 
Bit of a cheaper option which gets you access to a lot more games too.
Personally, I didn’t mind the Halo 5 campaign. I enjoy it for what it is.
I believe the fact that you only play as Master Chief for 3 missions is probably a big factor in why people didn’t like it.
The games marketing also led you to believe that Master Chief was being hunted by Locke. Which to some degree is true but the game didn’t really leverage that story much at all.
There’s also Warden Eternal; a boss you end up fighting a silly amount of times. Gets a bit tedious.
If you’re playing from a casual perspective you’ll enjoy the campaign. It’s fun and has some great action moments. If you’re deep into the Halo story and are super passionate about certain stuff the game might frustrate you with some scenes.
Generally though, it’s not actually all that bad.
My best advice is go into it with a fresh head and make your own opinions about it.
The main reason why I don’t enjoy the Halo 5 campaign so much is that the player has a so small margin of health and that many of the enemies can be considered as brutal. Wardens have a so powerful ranged attack that he can one shot the player, Hunters and many other enemies has a melee attack which is difficult to dodge and the player has a so low amount of health which in turn forces the player to use longer range weapons.
The experience of playing Halo 5 on Legendary is pretty similar to Halo 2 on Legendary if you wish to complete the game without being revived or being reliant on the revive mechanic.
It’s fun if you shut your mind to a lot of what makes Halo campaigns memorable. In the past, a good Halo campaign had:
fun gameplay
challenging and unique AI
plenty of ammo
music that doubled the quality of everything else
funny dialog from your allies
beautiful environments
excellent storytelling
Master Chief (save for Reach and ODST, where you still get awesome protagonists)
Halo 5 does gameplay (for campaign) and beautiful environments very well. Music is great, but doesn’t quite hit the bar set by Marty. Everything else is severely lacking. I can expand upon specific points if you would like me to. I also suggest getting Game Pass to play it first.
Translator
Halo 5 has a very good campaign, the difficulty makes you spend a few hours fun. It is not so difficult to complete it, additionally with the improvements of these Spartan it makes it easier for you to move through the maps, you will not have as many complications as in Halo 2 or Halo 3.
If you have Game Pass I recommend you take a look, if you are a fan of Halo play it, in addition to the campaign its multiplayer is complete. If it’s worth playing
The gameplay is cool, the movements abilities like thruster pack or ground pound are good novelty
In Halo 5, you always play with 3 allies, boots or real player, but never alone like in the other campaign.
Moreover, those three allies can save you from death, they have some seconds to reach you and cure you, it’s too easy
Like sayed before me, the only three missions xith chief and the bad promotion weren’t good for the game
Let’ s just say this: good ideas, good gameplay, spongy aliens, warden eternal.