WARNING: Wall of text ahead
You fracking jagoff! Haven’t you ever heard of a SPOILER ALERT! 
You’re not much better either, but at least I understand you’re replying to him…
That being said, as much as I like the story and the gameplay (both of which are absolutely fantastic), I do think the game is rather lacking.
There simply aren’t very many modes at all, for example. You get campaign (with co-op), multiplayer (with arena that has free-for-all, team slayer, capture the flag, breakout, and SWAT and then you also get Warzone), and theater mode. As @M00NLightNinja said, the Forge mode isn’t here yet. Although I don’t mind waiting, it is still a bit disappointing. Some multiplayer modes that are missing include oddball, juggernaut, and numerous others. What about Firefight mode with the waves of enemies to fight (Blue Team and Team Osiris would work well with this mode, I would think)?
The customization features are also lacking. Although there are a lot of options to choose from, it’s affectively hidden behind a pay/play wall and, as @M00NLightNinja also said, there are quite a few pieces missing from previous games that would’ve been nice to be included. Also, instead of being able to customize the head, torso, arms, and legs you can only customize the head and the rest of the body (since the torso, arms, and legs are now considered all 1 piece), which limits appearances.
Also limiting appearances are the emblems. In previous games, you could choose a foreground and background, and use 3 separate colors. Now, you can’t “create” your own emblem at all, but are instead forced to choose a pre-made 1. To make matters worse, when you choose the colors, you can’t choose any 3 colors you want, but are instead forced to choose from a set selection of 3 predetermined colors, which again, limits your customization. And yet again, certain emblems are absent from previous titles.
I also miss having certain class abilities to choose from that change-up the gameplay, like being able to reload faster from Halo 4, for example. I thought those kinds of things were really cool. Don’t get me wrong, I absolutely love the new game mechanics that should’ve been implemented as a standard a long time ago (aim down sights, sprinting, mantling, etc.), but I feel like they could’ve done more with it.
While the requisition system is pretty neat, I feel like it detracts from which weapons you can use, particularly in the arena modes. Certain weapons that you used to be able to see all of the time in multiplayer in previous games are almost never around in this game’s arena mode - for example, the needler and the SAW; the former only appears on 1 stage as far as I’ve seen and the latter doesn’t appear at all in ANY stage. This again, limits the game. That being said, I do like having the ability to have modified weapons in the warzone mode (just yesterday I was using an assault rifle with a long-range scope to snipe enemies with fully-automatic, accurate fire. 
As for warzone itself, I feel like it was hyped up a bit too much. I feel like there aren’t enough AI enemies (they only really appear during the beginning and during the occasional boss fight) and don’t really feel like a big enough threat on the level of say, the opposing team. The levels often also feel a bit too large and sparse compared to the arena maps, making traversing the map often a chore (not to mention boring to look at) and getting spotted (and subsequently killed) out in the open quite a pain. It doesn’t help that I’ve only seen 2 warzone maps so far after hours of playing the game, which yet again, puts limitations onto the game itself. While the requisition aspect works well here for the most part, I personally believe it’s also rather slow in earning the higher requistions, making the game mode rather boring overall because, to me at least, it seems to lose momentum as a result and lends itself to that boring traversal on foot that I was talking about.
The 1 thing I don’t like about the game the most is how they nerfed the motion sensor. You can no longer tell if the enemy is above or below you (which is a step back considering most of these Spartans are supposed to be top-of-the-line) AND the distance that it can detect enemies has been shortened! Instead of seeing out to 25-30 meters like it could before, it can only detect enemies within 18 meters of you. This limits your battlefield awareness so you can’t react in a timely manner, especially with the new abilities to sprint and spartan charge. They’re on top of you before you know it! This means you’re spending mroe time dying and wondering “where the heck did that come from!?” Even worse, this issue is compounded in warzone mode, due to its larger maps and long sightlines. To me, this is the ONLY issue I have with the gameplay, but sadly, it’s a big one. I liked having the extra range, as I favored an ambush style of play. I would roam the map and as soon as movement pinged on the motion sensor, I would get into a nearby corner and melee them as they came around the bend. Now, with the nerfed motion sensor, I can’t even get to the corner before being spotted. 
Another, albiet minor, issue I have with the game is how they’ve changed the appearance of a lot of things. I can understand they’re doing this to keep the series fresh, and that’s a good thing, but I feel as if they’re going a bit too far or are going in the wrong direction. For example, the rocket launcher looks NOTHING like it used to, which had a pretty iconic appearance. Even worse, many of the Spartan’s designs and vehicles (particularly the Covenant Wraith tank) look like they’re right out of Warframe, another sci-fi game that I absolutely hate BECAUSE of how it looks.
END RANT.
