Alright, here goes my response:
First, try to use paragraphs to separate your ideas. It also prevents "blocking" which just leads to people skipping what you wrote.
DMR controversy:
The DMR isn't classic, it was introduced in Reach, while the BR and carbine have been in Halo since Halo 2. In SWAT, the DMR and BR do the same damage, however they act differently. Both take one headshot to kill, or three chest shots. The DMR fires one round, which has a higher magnetism, but doesn't spread at all. The BR fires three rounds in a spread with less magnetism. With the DMR you have to almost be on their head to kill them, but with the BR, you can be farther off. However, since the BR does spread, it is not as effective at longer ranges. The DMR also has a higher rate of fire than the BR. The game is balanced, but when Halo 4 first came out, the DMR was much more powerful.
Flood Games:
I agree that the selection of flood gametypes in minimal, and the base gametype isn't very fun. The fact of the matter is, 343i screwed up majorly on gametypes. They left out assault, headhunter, stockpile, and one sided objective games (one flag, invasion, even firefight). For voting in matchmaking, wait a while for others to vote, if it is clear the game type you want won't get picked, you can still back out if you haven't voted.
Campaign and Spartan Ops:
Campaign was fun the first time, but doesn't have the same replayability factor that the other Halos have. It felt like Halo though, so it was fine. Spartan OPs was meant to replace firefight, and does a good job of it. I would want both next time around, but I won't complain if we don't have one or the other. In Spartan Ops, you always played as Crimson, and it was meant to be like "oh, my friends and I are Crimson." It was meant to be a transitional period between the Halo games. However, they stopped production for a second season of it, which sucks, because another season, even if it didn't progress they storyline would have opened up the Halo universe to a much larger scale (think about it, flood cleanup on a Halo Ring, Attacking Storm Covenant ships or bases, even fighting insurectionists).
DLC and Updates:
There are three DLC map packs currently out for a total of 9 maps, 6 medium/large and three small. Then add in a better forge map (forge island) and now two new medium sized maps coming out next week in addition to a new gametype plus two new armor abilities and more weapon and armor skins plus new armor in the Champions bundle for the equivalent of 800 MS points. The new maps are decent, and add some diversity to games. The updates happen every other week or so and are posted on Halowaypoint. Some are minor tweaks to maps and gametype, but others are much larger. Whenever a new gametype in matchmaking comes out, they release all of the schematics for the gametype in those updates as well.
So, do I think 343i could have done a better job? Yes, but they are starting to pick up the slack the last three months and are doing a good job of it. The next Halo game will be much better. As it happens, they were working on Spartan Assault earlier this year to release, so they were very busy in the past, but they can do a good job once they aren't preoccupied in three games (Halo 4, 5, and SA).