That pretty much summarizes my feelings on what I've seen of FFXV, too, especially when it comes to story and presentation. Like you mentioned, I was always one of those people who personally found the CG scenes in FF to be a nice little reward. (It got me through some lulls in FFXIII, lawd.) I know what they're going for with the Leviathan and Ardyn boss scenes, but I'm not sure if the issues outweigh the interactive advantages. I think Platinum Games have managed to achieve the right combination of snappy, interactive gameplay with a cinematic presentation, but they've understandably had a lot more experience.
Even though I'm frustrated by a lot of elements of what I've seen of the game, props to Tabata and BD2 for getting the game finished and released. I shudder to think of how exhausting the dev process behind all this has been. I hope poor Tabata gets a nice, long vacation and many cold beers.
I was really hoping she'd join the party at some point. I mean FFXV's a jrpg at heart. With how they were selling her, I was legit expecting a warrior princess. Some chick who'd be wrecking monsters, and that we'd be joining her fights.
In the end IMO, Luna is a fridged girl. She's there for Noctis to hate Ardyn as a plot point, and I'm a bit crushed about that.
It would have been cool to get her as party member, even temporarily, no doubt. Having obviously not played the game myself yet though, I'm not sure I agree she's a fridged girl because it seems like they actually give her and Noctis backstory and a relationship so her being a vessel for Noctis to hate Ardyn feels a little more earned than if it was just "So here's this no name princess you must marry for peace. She died...." but I guess it is semantics in a way.
I won't go into the discussion too much until the full game is out (well, that's kind of a lie after writing a few paragraphs later!), but Luna still sadly feels pretty fridged to me. They've tried to alleviate it somewhat by making her aware of her impending doom, and that she will knowingly sacrifice herself for Noctis - but that just feels like a bit of justification for the story beats, really. The fridge-ing is even worse in some ways because her character revolves around Noctis, which FF on a whole has surprisingly managed to avoid with its female leads. I feel like FFVII was the last one in the mainline games that was similar in role, with Tifa for Cloud. I feel like Luna plays an almost Serah like role in FFXV, as Serah was just a plot device to push Snow's and Lighting's motivations, and Serah getting ice cubed set the ball rolling for the main cast. (I'm trying to be hopeful, but I'm guessing Luna will have about the same amount of screen time that Serah did in FFXIII. Lots of flashbacks for Serah in XIII, too.) Luna has a bit more relevance and agency, at least, with her role as the Oracle + awakening the Astrals.
I was also a bit disappointed at the ending when Regis talks about Luna 'doing well to deliver the ring to Noctis'. After the absolute hell she went through, and her role as the Oracle, that's what she gets a mention for, delivering a ring? Obviously the ring was very important, but I also feels like it summarises the point of her character in both FFXV and Kingsglaive in a nut shell. A plot device primarily, character second. I know it's not fair to judge too much before the game is entirely out, but I feel like there is very little that can be added that changes the reality with the story beats of Luna's character.
I do really like Luna and Noctis as a couple (or really, the idea of them as a couple), and I think it's refreshingly cute that Noctis seems even more smitten with her than she with him. I guess with Squall/Rinoa, Zidane/Garnet, and Yuna/Tidus, we spend a lot of time seeing their relationships build. I don't mind having love interests that know each other prior to the story starting, but because of the small amount of time that Luna appears in the game, they've had to do a lot more telling than showing with their relationship. Even if there are flashbacks, or if Noctis spends a lot of time with Ghost!Luna after her death (please don't, I don't want Unchained Melody/Ghost flashbacks), I still can't imagine how it wouldn't feel comparatively a bit shallow.
A positive is that Luna doesn't feel as damsel in distress-y as she did in Kingsglaive. Props to the English version, too, as Amy Shiels did a wonderful job with the Leviathan scene and the confrontation with Ardyn. Darin De Paul is a bit of a force of nature, and I felt like Shiels easily held her own.
I'm really interested to know where Ravus and Gentiana were when Ardyn was pontificating and shanking Luna. Ravus was also in Altissia, wasn't he? I saw a screengrab with him and Ardyn. Ravus and Gentiana, you have failed terribly with protecting Luna. You're beyond fired. The Ravus/Luna interactions were my favorite part of the Judgment trailer, so I imagine her death isn't going to help those not-so warm and fuzzy feels that Ravus has towards Noctis and his family line. (...which, come to think of it, also gives another character plot motivation due to a fridged Luna. Sigh.)