I'll agree that the tutorial in Nier:A is somewhat jarringly simple. When the game put you in combat to start and just told you some button names, I was like "What? I'm already fighting!?"
On the other hand, I think this works alright since the combat is very open-ended (there's no "right" way to play, no scoring system, etc.), the game isn't very punishing on Normal / Easy, the buttons are largely intuitive in their function (fast attack / slow attack / shoot / dodge), and you can always go to the game's excellent menu to customize the controls in the way you see fit. I was surprised at how simple the tutorial was, but I also was surprised to find that it worked for me once I stopped being anxious and just went for it.
Contrast that with Bayonetta's much more extensive tutorial, which involves:
- a cinematic period where you can get used to hitting buttons
- a prologue chapter that throws small numbers of basic enemies at you (iirc you can't even die the first time you do it)
- frequently pauses the turtorial and has you practice actions one at a time
But Bayonetta's also much more challenging on its Normal difficulty, has a scoring system that gives you feedback, and has mechanics that aren't innately intuitive to people who are at least lightly familiar with video games (Witch Time, Bullet Climax, Charge Modifiers).
FFXV's tutorial was long and boring by comparison, but it needs that tutorial because the combat is so all over the place. Things like holding the Warp button to go to Warp points, cover restoring MP / HP, the dodge button being unresponsive (by design), magic recharge, and various mini-cutscene attacks that trigger under certain conditions mean that the game benefits from having a long, dry tutorial. Because none of that stuff is intuitive. If FFXV had no tutorial and just threw you into combat, people would constantly be asking questions about all of the above.
So yeah, basically, I understand where you're coming from on the tutorials. Nier's tutorial is somewhat unnervingly simple, but I think it actually works for this game. There's no ranking, there's no weird inputs, no right way to play, no conditional rules. It's literally just attack / dodge / shoot in whatever way works for you.
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And to answer your question about why your health was fluctuating: there's an ability you're equipped with that auto-uses healing items (their names pop up briefly when they get used). You can find it by looking around the menus.
I wouldn't be surprised if there's more instruction for the RPG aspects (like that auto-use healing item ability) in the full game. There just isn't much point in introducing it during the demo, since you can't actually do anything with it except turn off the HUD.