Thank you for the feedback and I'm super happy you liked the game!
Originally I actually had the running option in the game but it was way too fast for my taste and like a lot of your other issues, it got pushed further down the list of things to do because I was starting to run out of time. The Jungle map with the temple and the Gadget puzzle took much more time to make than I anticipated, so it was all time away from things like the coin collecting, which I actually added in on the last day since I did make the maps with those coins in mind and really wanted to get them in the game :)
Also the spearhead and the other ruby were planned to come in play later in the game when you get to the other islands and the temple to be a place where you keep returning and venturing deeper into. So, my thinking was that missing the other ruby and having that spearhead would tell the player that there is more planned but it just didn't make it in to the demo.
The dialogue is something that I feel I struggle the most with (from the actual dialogue to the formatting etc.) and it's definitely something I can improve in :)
But anyways, thanks again for the feedback! You have no idea how much it actually helps <3