Yeah I'm a solid 10 hours in myself. I'm having fun too. It's an addictive gameplay loop (especially as you unlock more options as far as traversal and tech), though we'll see if it manages to hold my interest more long term.
I'm really enjoying the setting, story, and characters too. It's some proper scifi.
I do have my complaints though. For one, the game is waaaaay too easy (I'm playing on hard). I steamrolled the beginning and the first boss without dying at all. I also didn't have too much trouble just bashing the shit out of mules to get through them. Thankfully though, this seems to have picked up in my current area. Mules have more tech and greater numbers, which makes fighting them a b*tch, even with my bola gun. I'm hoping the next boss is more difficult too.
The stealth sections with the BTs got old really quickly. I'm not a fan of playing minesweeper with enemies I can't see that don't do anything but float there and wait for you to walk into them. Even if they do catch you and start to drag you down, it's stupid easy to just shake them off and go about your business. These guys are more of an annoyance than anything (though the first encounter with them was pretty nerve wrecking).
The stealth in general is kind of poor. Mules have eagle eyes that spot you from a mile away even crouched, and walking/running sound doesn't seem to have much if any impact. So far, stealth doesn't even seem worth the effort, which is insane considering the series Kojima is known for.
Thankfully the traversal and delivery mechanics are fantastic, which is good since that's the entire point of the game. I like that Kojima tried something completely new, and I'm enjoying it. I also can't help but feel that I would have enjoyed better stealth implementation. MGSVs stealth with the traversal and changing world in this game would have been perfect. Build a little off what you're good at, Kojima.