I have a level 68 Noctis, currently, and I still haven't really done everything in the game (fighting the Adamantoise was a 3 hour chore, but I got an item that gives 10000 HP for the trouble; so, it balances to some degree, in my book). Is FFXV a great game of epic proportions living up to the hype and run-up to the release? No, not in my opinion. Is it a complete and horrible dribble that one should steer far clear of? No, not in my opinion. It's an okay game with some gem moments and a bunch of warts. Honestly, I can say that I've had fun with it, considering that I've put 90+ hours into the game.
It is true that the story is a bit thin. This is not because there isn't a story or that it is incoherent. It's more that the story, in its full completeness, is not told. You get more the major plot points, but missing is all the extra fleshing that would fill out the story. There isn't as much character development in the game as I personally would like to see for a story driven game (although, Noctis does become less a douche at the end, so that's some development), but there is some if you're paying attention to the dialog along the way, especially in the latter half of the game (also, me being a much older gamer, my tastes tend to lean toward more nuanced and subtle content, but I'm also fine with just mindless head-bashing every so often). I'm not going to lie; if you just jump into FFXV without watching the Brotherhood videos (available on YouTube) and the Kingsglaive movie (which is actually a fairly good action movie and well worth a rental, which is what I did), you may feel lost or emotionally detached from what is really going on. Brotherhood and Kingsglaive put the story of the game into better context. However, I will admit, having said that, in my opinion, this is not really a good way to tell a story in a video game. The story of the game should be fully in the game and not require me to seek external sources to fully understand or appreciate the story (or, looking at you Destiny, even to tell some semblance of a story in the first place, even if as a loose collection of author's notes; but we understand that you don't even have time to explain why you don't have time to explain). But even given that, you are told enough of something of a story to at least put your actions in the latter half of the game into some context. It's just that context is much more fulfilled if you've watched the YouTube anime episodes and the movie. For instance, unless you watch Kingsglaive, you probably won't get a full sense of the treachery that the Empire pulled in attacking Lucis or of the desperation and self-sacrifice of King Regis in attempt to save his kingdom and thwart the Emperor's ultimate goal. Yes, I will wholly admit that all that would have been much better placed directly in the game and played out in its full glory within the game. The emotional impact would have been so much greater (in fact, I would dare say many would probably have to take moments to put down the controller and step away from the game just to sort out their own feelings before returning to the rest of the game).
As an aside, to answer Fox12's complaint about learning that Noctis' father had actually sent him away, this actually is revealed in the game. I won't say where or how to avoid spoilers, but it is in there.
You can play the game as a straight progression along the major story quests, which are clearly denoted from the side quest, or you can spend your time faffing about on side quests and fishing, which is a lot of what I did. Yes, spending a lot of time on the side quests does break the pacing and sense of urgency of the main story quest, but I did so knowing that that would be the case. So, for me, immersion was not broken because I didn't play the game in such a manner with any expectation of such immersion.
To be fair, I think it impossible (or, at least, extremely difficult) to have a fully free-roaming, open-world environment and still enforce a singular story plot without some significant compromise. You're either going to have severe disruptions of pacing or severe constraining of the open-world environment such to force the player back onto the rails of the main story. I suppose one could introduce some parallelism in which key events continue to happen on a well-defined timeline (in game time), and those key events have drastic effects on the nature of the game depending on whether the player dealt with them in time or not. But, then, I could see people complaining about that as being the game forcing them to do something they don't want to do. Or, you could simply have moments where, if you initiate a particular story quest, you are forced to complete that story quest and can do nothing else (this is, in fact, what happens in the latter parts of the game). But, doing so is a case of removing the open-world aspects for the sake of story progression in that singular instance. Once the quest is complete, you may be given access to the open-world aspects once again because there is no longer an urgency to progress the story (again, this is exactly what happens in the game).
To be honest, I think my only real complaints for FFXV is that the story needs to be fleshed out more than just delivering main plot points. Also, there are some performance issues and glitches that can cause the game to crash (yes, I am playing it on PS4 Pro, and the performance issues look to me to be more the software than the hardware). While Square-Enix played this up as a next-gen game, to me, the game's graphics look more like it was originally targeting PS3 and Xbox 360 and got hurriedly upscaled for PS4 and Xbox One. Otherwise, I've enjoyed the game. Considering that I've put 95+ hours into it, I'd say I've gotten my $60 worth of entertainment. Could it be far better than what it is? Absolutely. Is it a complete turd of a game? No, not in my opinion.