Yeah, the terrain system was one that really needed some hero pieces and variation for signposting. A mini or full map would have been a good plan too, unfortunately I really ran out of time having just cobbled together the bare minimum.
The fuel was originally going to be used as mana for special attacks, and would have tied into a special attack called "piercing" which would cause a status condition with you leaking fuel until fully repaired, and also made you super vulnerable to fire damage. As it stands, I agree that fuel doesn't add that much to moment to moment gameplay.
The lack of saving was because the game was originally going to be a roguelike, with procedural generation of terrain and enemy placement. Also I didn't have a clue how to properly serialize and deserialize all the data in to save files...again I wish I'd had more time to implement this.
The enemy balance was due to my combat code being wrong for most of the dev time, since I was working on other systems and thought it was producing the correct results. The last two days was a ton of going to and fro between too hard and too easy, and I erred on the too hard side, since earlier on one of the testers felt that there had been very little challenge in the game.
Aye, it needs a lot of work, thanks for your feedback!