Something isn't inherently better because it's newer, but neither is something inherently better because it's older. There's a reason why both appeal to novelty and appeal to tradition are both fallacies. The relative merits of a change or a new thing should be evaluated on its own merits.

Since we're talking about gameplay stuff, let's focus on that for a bit, specifically player movement in Halo. When the series first started, the basic means of moving your avatar (usu. the Chief) was a very simple and straightforward affair. You used the left analog stick to walk/run, you clicked left stick to crouch, you use right stick to turn around, and you used a face button (usu. A) to jump. So, your entire range of movement is dictated by the analog sticks and one face button. That's pretty much it for basic movement. Pretty standard stuff for an FPS. It worked like that for four consecutive games. But over time that minimalist approach has given way to greater complexity.

It first started with Reach and the addition of armor abilities, some of which changed how you normally move. Sprint allowed for a few seconds of increased running speed, jet packs allowed for flight, and Elites had a combat roll for quick dodges. But you could only equip one ability at a time and they were optional. Nevertheless, sprint, jetpacks, and rolling were additional complications that you had to keep track of.

Halo 4 made sprint standard but still kept armor abilities, thus adding an additional layer of complexity. In addition to walking, turning, and crouching you now pretty much had to utilize sprint to traverse maps in a timely fashion, engage in combat, or retreat from enemies. But you also had to keep track of the ability to either fly or thrust strafe, depending on if you had either the jet pack or thruster pack.

Now Halo 5 comes along and ups the complexity even further. Sprint is still a standard ability (and is now unlimited, while in previous games it had a cool-down period after a few seconds of use, barring the use of the Mobility perk in H4), and while armor abilities are gone "Spartan abilities" are now a thing. In addition to walking, turning, crouching, and sprinting, you have thrust strafing, hovering, sliding, clambering, and ground pounding (which is both a new form of movement and an attack), all as default forms of moving and traversing the environment. This is by far the most complex and maximalist Halo game ever when it comes to just negotiating your Spartan around the battlefield.

These changes to have an undeniable and far-reaching effect to gameplay beyond simply complicating basic movement. It affects map design as the environments have to be designed around how the player character moves. It also affects the flow and pace of combat; Halo was originally a game with a fairly leisurely pace (as compared to FPSs of the 90s, which were often much zippier), but sprint speeds it up and now default thrust strafing speeds it up even more. Now, your mileage may vary if these changes are good or not. Personally, I think Halo 5's maximalist approach to player movement makes it feel not all that much like a Halo game. Part of the appeal of Halo was its simplicity and how it was still able to offer deep gameplay with said simplicity. Basically, Halo epitomized "easy to learn; hard to master" design; instead of bogging you down with overly complex gameplay, everything was simple, deliberate, and measured. It was less Radiant Silvergun and more Ikaruga. When I played the Halo 5 beta, it felt overly complex and fast-paced. Not only was I having to deal with Spartans darting around the maps at breakneck speeds by Halo standards, I was also having to keep track of the myriad abilities at my disposal. It seems that modern shooter design necessitates ever more complex and fast-paced forms of movement, as seen in recent games like CoD: Advanced Warfare and Titanfall. Indeed, Spartan Abilities are mostly forms of movement that already existed in other shooters. This is ostensibly to make the player "feel" like they're actually playing as a supersoldier, but the end results is a game that "feels" very, very different from every previous Halo game.

I don't mind change, but I do mind change for the sake of change. I believe a developer working on a long-running franchise should keep what works and improve or discard what doesn't work. Refine the gameplay. Don't reinvent the wheel, leave well enough alone, and if it ain't broke don't fix it. Discarding perks and rank-based unlocks was a good change (it discards a previous bad change introduced in Halo 4) and I applaud 343i for bringing back the level playing field, but the radical changes to core player movement is a change I'm not particularly fond of. There are several other changes that I think would have benefited the series to a greater degree:

1) Level design in Campaign has stagnated and in some ways gotten worse, becoming more linear and constrained with fewer opportunities for exploration, sequence-breaking, or otherwise going off the beaten path. Despite the 360 being more powerful than the OG Xbox, I found it interesting that that additional power wasn't used to make more expansive levels. AotCR still remains the pinnacle of large-scale level design in Halo, while Halo 4 is perhaps the most linear and constrained in the series.

2) AI and encounter design could be refined to make for more interesting and legitimately challenging (as opposed to merely punishing) battles.

3) If the Promethans return, they could find ways to make them more interesting enemies and refine their weapon sandbox to make some truly unique an interesting implements of war from a truly advanced civilization (as opposed to copies of UNSC & Covie weapons that simply fired orange bullets).

4) They could push the boundaries of what Forge is capable of as a map editor, going far beyond the simple ability to move building blocks around in an otherwise fixed environment. Giving us tools like the ability to set environment type, time of day, weather conditions, and even deform the environment itself would be major improvements. Basically, combine the best of Forge with the best of the Far Cry map editor.

Halo should evolve, but it should do so in the right way, and quite frankly I don't think it is.