I'm sure you've gotten some or all of these suggestions before, but I've thought of a few things I'd really like to see in the game.
- A softcore mode - I like the perma death style for this game. I think it really fits the theme and makes you try harder to avoid damage and play strategically. But a more "relaxed" game mode might be nice at times. I'm not much a fan of perma death games, so maybe it's just me, but after playing perma death for awhile I just get bored of starting over and whatnot
- Farther progression - I assume you're already thinking about this one, because as of now the game feels quite short. When I reached the final boss I felt pretty under powered. Perhaps you wanted it to be this way? To Incite a feeling of challenge or fear into the player. Either way, I never got the feeling of owning a "powerful" island. I like to play games up until the point where I feel unstoppable, where I can beat pretty much anything with ease. Even if this was just in an 'after the final boss' free-play mode, I think it would be a satisfying addition. Additionally, when the player chooses a new game, perhaps they could choose between different game lengths (3 portals, 5 portals, 10 portals, etc.) with varying difficulty of final bosses. This could give players a quick game which is challenging with few resources, or a long game where they can heavily customize their island and improve its features.
Hope my suggestions give you some ideas!