Oh, where to begin?
All of your first five examples have already been thoroughly explained before Halo 4 was released. Hard-light has always been a thing, The Storm would gladly follow the Didactic, and much of the non-Storm covenant as well. Imagine God coming to Earth. Much of the other stuff was explained in the many Halo novels that have been written. Lots of people liked that Halo 4 actually made an effort to incorporate the backstory instead of completely disregarding it, much like Reach did.
Part 2: Halo 4 was not supposed to be pretty. The other Halo games could get away with pretty because pretty landscape in games usually begets an upbeat ending. Halo 4's ending was anything but.
Part 3: forerunner buildings have lights everywhere because an actual, living Forerunner is now running them. Everyone in the UNSC has had an American accent for a long time. It's no more immersion breaking than the fact that everyone in Ender's Game, including four-year-olds, could speak perfect English, no matter what country they came from. All MJOLNIR armor has been pretty much the same since Mark V armor (which was the first successful generation of MJOLNIR, mind you), and all resulting generations were based on it. It makes sense for the Pelican and Warthog to have changed radically, don't forget this game is set YEARS after Halo 3. The wealth of Forerunner tech at Onyx, combined with Cortana's intel, certainly begets changes in design. You also mentioned that you like scientific explanation that Bungie apparently used. But you complain about the design of the plasma weapons that, not only makes scientific sense, but is also largely unchanged since Halo 1.
343 did not want to insult Bungie. In fact, many employees at 343 are former members of Bungie's Halo dev team. 343 was formed because Bungie was leaving Halo, but the debs didn't want to.
Halo 4 DOES take a tad too much inspiritation from COD for my taste, but it makes sense. It's 343's first game, and they needed to prove to investors and publishers that they could make a game that sold well, and had mass-market appeal. They also needed capital to continue developing. It would make sense to not see any major changes until Halo 5.
Overall, cutting out Firefight was a bad move, I miss the weapons being scattered across the map (although it DOES do a good job of preventing one team from hogging all of the power weapons.), ordinance drops I have mixed opinions, Reach is still a piece of shit sorry excuse for a game, and READ THE F****** BOOKS the game is based on before complaining about the story.