Still not a fan. In addition to the tonal issue noted in the OP, there's also the major issue of narrative consistency and foreshadowing. As I believe I mentioned in a prior discussion, this is a story where the two greatest weapons at the antagonists disposal were 1) the element of surprise that allowed them to cripple the galactic war effort before the galaxy even knew it was at war by destroying their leadership and isolating the planets from reinforcements, and 2) is their ability to corrupt their opposition, to break their minds and turn them to their way of thinking.
The first advantaged was nullified in the backstory, as was laid out in the first game, and the second featured prominently in all three games as core aspects of the major antagonists. Benezia, Saren, the Collectors, Cerberus (as of ME3, at least in the knock-off sense), and even that Hanar "Regards the Works of the Enkindlers with Despair" all beautifully illustrated the concept across the franchise. It's also heavily implied that the Rachni of a few centuries prior also fell victim to indoctrination, leading to the Rachni wars of the backstory, to say nothing of the fact that every single hostile Geth you face in the main games (Overlord being the sole exception I recall) is also fighting on behalf of the Reapers who treat them as disposable tools.
This is an enemy who weaponized brainwashing, consistently creating other antagonists for the galaxy by converting others to their way of thinking. And that is not treated as a matter of charisma or having a sympathetic cause, mind you. That's consistently treated as "they will twist your mind until it rationalizes service to them as an intrinsic good", as was so aptly spelled out by Benezia in the first game[footnote]"The longer you stay aboard [Sovereign], the longer Saren's will seems correct. You sit at his feet and smile as his words pour into you. It is subtle at first. I thought I could resist, but instead I became a willing tool eager to serve."[/footnote] and further illustrated by the justifications of the aforementioned indoctrinated antagonists. Cue the finale and the villain turns the charm on Shephard and tries to get Shepard to embrace that same (apparently luddite) ideology in the last five minutes of gameplay, with agreement with that ideology apparently being the authors' idea of a "golden" ending...which is to say that instead of acting as a foil to the series' antagonists, the preferred ending has Shepard echoing and validating those antagonists.
And then we get the foreshadowing bit. As priorly mentioned, one of the greatest assets available to the Reapers was their ability to assassinate the galactic leaders and isolate the worlds before anyone even knew what was going on, an asset which they no longer had access to because of the Citadel being isolated from their control, Shepard being forewarned about them, and the galaxy having an abnormally high amount of experience with Reapers and their tactics before they could properly invade. From the get-go, ME3 has already set up the storyline as the Reapers' best laid plans finally falling apart, with both their regular strategy and their contingency failing, both eliminating key advantages possessed by the Reapers and giving the galaxy an unprecedented technological and tactical boost which helps to minimize the raw power difference that the Reapers are then forced to rely upon. ME3 was the culmination of the absolute worst case scenario for the Reapers.
Then the game starts and we start getting hints about what does and does not work against them, with certain key moments including the destruction of Reapers on both Tuchanka and Rannoch. Codex entries offer similar gems which suggest things were possibly going worse for the Reapers than it first appeared, with the golden ending for Rannoch (peace with the Quarians and Geth) noting that the Reapers were likely not to have even considered the possibility of the combined might of the Quarians and Geth armadas, much less likely to be prepared to deal with them. The Miracle at Palaven entry showcased the Reapers being outmaneuvered tactically and lost processing ships, troop transports, destroyers, and even capital ships as a result. There's a dedicated codex entry for Reaper Weaknesses, which specifically notes that "theoretically, with the right intelligence, weapons, and strategy, the Reapers could be defeated" before proceeding to outline possible exploits against them ranging from what weapons are most effective to trade-offs the Reapers make for situational advantages[footnote]Their systems allow them to pull against their defensive abilities to grant them greater turning speed, for instance[/footnote]. And during the final push Javik notes that the Victory Fleet was beyond anything the Reapers had likely ever faced and that its diversity gave it a further advantage that his own cycle had lacked. Heck, even the Multiplayer screen hits a point where it says that "allied forces are holding fast and winning in key areas".
Narratively speaking, the story had been pushing the idea that while the Reapers were an incredibly powerful foe, they were pretty much at the weakest they had ever been and the Galaxy was at its strongest, that for the first time in history victory against them was possible. Almost certainly costly, but possible. And then it doesn't go anywhere with it. It builds up and then falls flat. Every single advantage shown, discussed, and present in the codex is ignored in the final act. Reaper shields are significantly weaker near a planet? Fight them in orbit! Reaper Capital ships can't withstand the firepower of about 4 dreadnaughts? Don't focus fire, spread shot! Strategy? Pah, forget about it! Just go for overwhelming force despite the Reapers having raw power on their side! Diversity breeds strength? Let the humans control the battle, and make sure that only humans are represented among the ground forces! Don't forget to bet EVERYTHING on that [presumed] superweapon that we don't know the purpose of or how to use instead of fighting to win in case it doesn't pan out. I swear, the final act had the entire cast playing keep away with the idiot ball to force the writers' pet endings which themselves were not tonally consistent with the rest of the series. They simply were not a natural culmination of the story.