Halo CE: Pros- Gameplay. Universe. Story. A.I… Enemy action/reaction and three way combat. Great ending sequence. Characters. Fantastic music.
Cons: Backtracking. Some invincible vehicles. Install kill vehicle nudges.
Halo 2: Pro: Story. Dual sided campaign. Vehicle play. Continuation of plot and increased size of problem. (All haloss activated and on standby. Gravemind.) New enemies. (Brutes, charging punks. Scarabs.) Enjoyable boss battle at the end. New weapons. New Covenant characters, who were likable. Playable Elites.
Cons: Short story, cliffhanger ending. Dual wielding. Didn’t add much. Addition of BR. A few exploit glitches. Bxr I think it’s called. Lotsa magnetism.
Halo 3: Pros: Campaign levels. Fun, large, varied environments. Vehicles were great. New vehicles and new enemy types. New weapons. Increased player customization. Visible alternate weapon. Addition of Forge. Theatre mode. Helping Machinima. New multiplayer types.
Cons: Really underwhelming and boring story. I’d even say bad. Cortana not detonating the Halo ring to stop the Flood from getting away. Master Chief having some kind of Cortana spam virus thingy. Pointless character deaths. Underused villains who kinda just interact with you once then you go on until you kill them. Terrible final boss. Floaty jump physics. Multiplayer Achievements. Under used allied characters, faction. (Arbiter, Elites.)
Halo ODST: Pros: A cast of likable protagonists, a new cast and main protagonist. Firefight. Removal of dual wielding. Open world exploration. Another look at a Covenant species. Shows Spartans aren’t the only cool guys in the universe. Conveyed threat of Brutes well, showed believable character injury as well. New enemy interaction. (Engineer shields.)
Cons: No match making for Firefight. Over priced. Pretty short. Unexplained protagonist ESP abilities.
Halo Reach: Pros: The best player customization in Halo yet. Addition of function and play style to Firefight. Addition of fun assassination animations. Entirely optional as well. New weapons and vehicles, new enemy type. New style of play. (Space combat.) New abilities to change how you play. (AA’s.) New multiplayer types. (Invasion was fantastic.) Persistent character customization in all modes. A new cast of character and introduction of Halsey from books. Dramatic storyline, all too often we never fail as MC, but this shows the downside and more believable side of the war when you’re always fighting a losing battle. Shows how Spartans would sacrifice themselves for the greater good. (Jorge. Noble 6. Carter.) Good new music. A absolutely fantastic ending to the game. Robust forging system.
Cons: Lack of character development for Spartans, lacking the dramatic sting that should have been displayed. But over the course of a eight hour shooter with a large focus on multiplayer, necessary evil. Issues with AA’s, but first go and not terrible. Loadout system kept most people on a even level, but allowed variety with AA usage. Lack of a good vehicle level. Spoiled end at the very beginning.
Halo 4: Pros: New weapons. New enemy types. A more dramatic focus on Cortana and MC. (Though, this was only possible due to the prior Halo 1-3 games. Without those, this story would have been laughable underwhelming.) New characters. New Elite villain. Dramatic twists.
Cons: Terrible Promethean villain. Unexplained force powers, Unexplained prison ball that can be used by said prisoner as a ship, and as a bridge for a even bigger ship. Covenant remnant being entirely unexplained. Worsened art style. Removal of Firefight. Spartan Ops being online only. Lessened multiplayer suite. Unnecessary loadout and level system. Bad unlock system. Short campaign. A.i. Unimpactful music. Two uninteresting driving segments. (Plane. Ghost.) Ordnance system.
In closing: No, I didn’t cover everything, but this is the things that kinda of popped up in my head when thinking about these games. Kinda didn’t say much on music because only CE and Reach have tracks I explicitly remember. xD And I haven’t done enough on Wars to throw that out here.
I know the dislike of BR is entirely my opinion, but I had to throw it in there.