Sorry for another rant in advance.
I think the worst thing about the multiplayer in this game, and why I'd never actually regard it as highly as other popular online shooters, is because the vast majority of deaths and kills are not well earned or deserved. If it's not you immediately getting caught completely unaware because of the ridiculously inept spawn system, it's you getting one shotted by a power weapons of some sort, generally also completely oblivious to where the shot came from, because you never saw the enemy in the first place!
Only a minority of the time (in Arena) is a death ever from just an ordinary 1v1 engagement, and even when it is, weapon variable often plays a bigger role than actual aiming skill. Like, I happen to bump in to someone whilst armed with an SMG whilst he has an AR, he's dead pretty much guaranteed. I run in to someone who's quite far away, armed with an AR whilst he has a BR, if I have no where to run, even if I whip out my pistol it's pretty much a guaranteed death because in that time he'll have fired enough shots to weaken or kill me. So in that sense the skill factor in Halo 5 is surprisingly low, unless you happen to bump in to someone with the same weapon where neither of you had a one up on spotting the other first. Otherwise weapons have very specific categories of range, and that messes the flow of combat and quality of engagements.
As I'm getting to higher levels, I'm noticing an increasing volume of my deaths are from one shot power weapons. Other games have this issue, such as Destiny for example with super powers, or COD with snipers, I think the difference in Halo 5, and what makes it much worse, is that spawns are well placed in Destiny and COD, you're often put closer to your own people, and not often immediately in harms way (less so in COD, not at all in AW). Halo 5 in Arena at least, is the complete opposite. It will spawn you wherever the hell it wants, whether that's directly behind an enemy, in front of one, in the middle of a bunch of enemies or whatever else, the game doesn't care. Add to that, the lack of kill cam means partied up groups can camp certain spots a little easier.
I'm definitely interested to see how the legs are on this multiplayer, but my guess is player numbers will drop off fairly quickly over time, and level out at something fairly low for Halo standards. There's just so much about the multiplayer that is unbalanced or that needs work. There seems to be less priority given to simple combat engagement and aiming skill in this, than any other online shooter I've played in years. So many variables detract from the fundamental aspect of just shooting standard weapons, or having fair engagements.