Q-Vier finally got what he deserved, which is a good thing, and the battle with Cain was alright, even with the typical friendship speech involved. Can't say I'm much of a fan of his robot's design, but at least it came across as enough of a threat. I'd say Haruto and L-Elf had a pretty nicely done final scene together too. The most cynical folks can make crude jokes about it and all, but that doesn't really matter to me. That said, I was never a big fan of the protagonist himself either and it's hard to get truly emotional over it. I suppose it also works as a fitting end because we could see this sort of resolution coming, especially given the precedent of Marie's fate and the increasing rate of memory loss.
Concerning the future content, I wasn't expecting much more than a short epilogue with Saki and the kid, so that's basically what happened after a brief montage. Oh, but who could possibly be that little boy, the Prince? All things considered, he should be a descendant of L-Elf, given the obvious physical resemblance and what a couple of other throwaway scenes implied. I'm not losing any sleep over not having an explicit confirmation of his identity though. It's almost besides the point.
In the end, I would say the effective role of the flashforwards was just to be a partial framing device and as confirmation that somehow, someday L-Elf and the other Space Vampire folks were able to fulfill that final pact with Haruto on the moon, even if this show obviously couldn't portray the whole process within the allocated time. Which is a shame, since that empire-building phase could have been potentially more interesting than the rest of the story. I guess that's the typical fate of many series that were effectively cancelled when they were just getting to the most promising stuff, so to speak, and Valvrave isn't any different.
Now, this does leave the one future scene from episode 7, which suggested a new conflict with an unknown enemy came about, as an unused hook for a sequel that isn't going to happen. Can't deny it comes across as sloppy and disappointing, but pragmatically speaking...I can't see how they could try to address that now and not make things worse. You either follow it up with another season, or there's no point. That said, I'd argue episode 23 had already made it sufficiently clear what promise Saki was still trying to fulfill, so the whole bit with the pendant isn't much of a mystery at all. Who else could be in the pendant but Haruto himself?
In terms of what happened with the Magius threat in the present and so on, that's another part of the ending that was evidently rushed through. They weren't really great enemies or anything, but it's not particularly satisfying to see them get wiped away in seconds, even if the narration explains this actually happened after a fair amount of time. I'll admit the concept of ARUS turning against them still works, at least in theory, but this really needed a lot more screen time or, again, part of another season.
One of the other things which seems to have enraged some folks is what happened to Shoko, since the masses were clamoring for her death for no good reason, but I felt the character's new role is appropriate despite the cheesy nature of the scene and the final message. She realized her attitude towards Haruto was wrong and tried to make something constructive with her life in his name. The usual stuff.