Main issue here, either stop or toggle the feature of joining games that are almost done, halfway through, or even a couple minutes into the game. This is Halo, not CoD, and Halo should ALWAYS start games from the begginning, we have custom games for joining. I can not count the amount of times I've been put into one sided games which just add to my list of lost games.
Weapons on the map. The idea of power weapons being on the map and randomly respawning is awesome, but what about the weapons you start of with? Like many others, I find myself runing out of ammunition quite often, left with the choice of having to scavange for other peoples weapons which results in death most of the time. Bring back loadout weapons to the map, at a constant spawn so people can learn their spawn, but leave the power weapons at random.
Vehicles are way to destructive. I love the idea, but it does make them quite useless. All a person has to do to a warthog is stick it and boom, double kill!
XP cap, are you really discouraging your players from playing the game? Seriously, reaching 150k xp in a day is quite impossible unless you play all day, but even when you do, people find themselves having to wait hours before they can play after the midnigh reset. You dont want people getting ahead of others, well thats their deal nobody really complains and im sure the lower level people dont complain either. If your main concern was for the little guy, you're also limiting them. If you keep the XP cap just so the little guy can "catch" up, they too will eventually reach the cap and be stuck with having to wait till they can start earning XP again. Reward your players, not punish them. XP cap, really, who does that?
Playlist. I know you added SWAT, but there should have been way more options at launch then what you offered. The amount of playable options is what made the Halo multiplayer legendary, dont ruin it.
Assassination glitch. Its happened to me a few times where, like mentioned previously, the animation will stop and the person being assassinated will temporarily walk out of it and be given the chance to fight back. Even though eventually they will die to the assassin, they shouldnt be allowed to get out of it to fight back lol.
Lastly, fix your servers. I, like many others, have been victims to your server crashes where we are reverted back to level 1 and we can not join other regular people and we're stuck with playing playlists with no more then 100 people. With an added after effect, your loadouts tend to reset when things go back to normal.
And those are my two cents. Most of the stuff has been said before, but I'd like to reinforce them and seriously bring them to your concern.
