Your game actually reminds me quite a bit of two older games: "Indiana Jones and His Desktop Adventures" and "Yoda Stories" (built using the same engine). They're both mouse-driven, coffeebreak style, procedurally generated fetch-quests.
First of all, replace the weird mouse-based movement system with conventional keyboard controls. That will feel much nicer, and also allow for some other improvements.
Secondly, right now, gameplay consists of fetching items in order to either exchange them for other items, or to unlock portals. This quickly starts to feel repetitive. There needs to be some element of skill - typically, in top-down games, that means combat, with monsters that actually fight back! (if it were a side-view game, there would be platforming elements to provide additional challenge)
Zelda-likes and Metroidvania games are also full of more interesting types of gates/locks/keys/valves, which you could incorporate.
For example, the classic block-pushing puzzle. The player encounters some large immovable boulders blocking their path. The player needs to find a specific item, which gives them the ability to push heavy objects (including, but not limited to boulders - it's good to make items multi-use). They then need to use this ability to solve a Sokoban-like puzzle by pushing the boulders in a particular way.
The RPG "Golden Sun" has loads of magic skills which can be learned, and which not only help in combat, but can also be used to solve puzzles.
Another example, might be an enemy that is very resistant to the player's attacks. It could be either a single boss monster, or a particular type of monster that becomes very common in an area, but either way, they would effectively be forming a locked gate. If the player attempted to continue, they would be expected to die, so instead, they must first go find a particular weapon, which is more effective. Having said that, an extremely experienced player might be able to bypass that section of the game if they can defeat the monsters using pure skill (speedrunners love this). This is one of the areas where better player controls would be required.
In the game "Zeliard" (probably the best metroidvania there is), there are heaps of great examples. There are ice caverns, where the floor is slippery, making the tougher platforming sections almost impossible. It is expected that the player will seek out the special shoes which allow them to move normally on ice - but actually, a very skilled player can get through that section of the game without the shoes.
The other things I mentioned were valves. These are basically one-way shortcuts, and they make back-tracking much easier for players.