[SPOILERS] My many issues with this rushed movie

RazielZero said:

1. Black ash is what remains of the Elementals (the race itself) when they are destroyed (or die or whatever they do). These are poisonous to many races, and especially to the frail humans, so that's why they use masks and gloves to so they don't come into contact with it. Since the black ash is magical, it can be used by humans to hide their identity, since the elves (and warbeasts for example) can't "see" what kind of race they are. Their sight is blocked off by the magic.
This was only hinted in the movie, though I guess it could have been explained a litte better.

2. Riku was a regular human child. Tet was his imaginary friend back then, someone he imagined to be the "ultimate gamer", since the played alone.

3. Riku knew Schwi didn't just mean to kill random humans by reflecting that attack. He know what part the Ex-Machina played in the war, but he still loves Schwi for who she is (and who she became thanks to Riku). Also, a whole year has passed since they first met (which wasn't explained, only hinted by the montage of the ghost team's operations), so that's quite enough time to develop feelings for someone.

4. The old deus are probably not all-knowing at all. They seem to be representing aspects/concepts like Artosh being the god of war and Tet being the god of games/play. They are probably foolish in their own way, only caring about being able to rule the world by force and by the races they created, eliminating everyone else and thus becoming the One True God.

5. Like you said, Riku's plan was to manipulate all the races/gods from behind the scenes. They would make them use their powers against each other in one final strike, so that they can use those orbs to redirect all of it into the planet, thus destroying it and subsequently summoning the Suniaster, since what else would be better in showing the "ultimate power" than destroying the planet itself (and not simply by killing everyone else). His plan almost failed due to Schwi getting killed and not being able to finish planting all of those orbs, only 2/3 or so of them. The rest of the Ex-Machina helped him by using those to at least steer the orb into their direction so that they could absorb/analyze it and replicate it for Riku.

6. Riku couldn't take the Suniaster since his only remaining hand literally burned off (either because of the power released by the ongoing destruction of the planet or because the Suniaster itself is that powerful for a mere human). He pleaded and prayed in his last moments for someone, anyone to take it and stop this unnecessary war, as he felt physically and mentally unworthy of it, having sacrificed so many people (and Ex-Machina) for it. His strong prayer summoned Tet, his imaginary friend, hinting that probably all old deus were brought forth from concepts and ideas (like war, knowledge, etc). Tet is kind of an old deus in this way, but only for those few seconds before he became the One True God.
The other old deus were probably unable to just simply teleport there and take it. I'm not sure about that unfortunately. But it's irrelevant.

7. It's not Earth, but we (or at least I) don't know much about the other planets. All we know from the movie is that most of the other races came here during the great war, as it was originally the planet of the humans (or maybe some other races as well). Tet might be ruling over the entire universe, and maybe even the multiverse if our Earth is just a parallel to this one.

Now I haven't actually read the novels, and only looked up a few minor things, but almost all of these were from the knowledge I gathered while watching the original series and the movie. Maybe they weren't clear enough for you, but I think the movie was quite well paced, and everything necessary was explained well. I'm sure there were things left out, but apart from the actual properites of the black ash and the 1 year skip everything else was clear in my opinion.