Holy crap, this is very... Advanced, I actually never knew flash games could get this thorough, nevertheless, it's a very good game in all, it seems to have a terraria-MC vibe which is very good, I played a good hour on this and had a spectacular time.
Bugs:
Block Clipping:
Sometimes i'd go through blocks, not the background ones, actual wooden planks at times, though this isn't that bad since you do not suffocate, but it can become a nuisance in certain situations.
Hit range: I don't know if this is a bug, but sometimes when I hit, in the direction of the creature, it does not hit, is there a hit/miss system? Or is the combat a WIP?
Block mis-conception:
Not really a bug, but a VERY big personal issue, for E.G, the wooden planks, the background version looks pretty much the same, so I get mixed up, I accidently made my house out of the background blocks and then discovered I can walk through the entire thing :P
Suggestions:
Multiplayer - 'Nuff said. I know you've already stated you'd implement it in the sequel, but think of this as a reminder :P
Also, incorporate a server browser and attempt to have Dedicated servers for every MC/MB genre, like Survival, PvP, Competitive Survival (Survival PvP), Creative, Friendly Survival.
Difficulty levels - Moar difficulty levels, like Lonely/Peaceful/Easy/Normal/Hard, just so it's a bit harder.
Hardcore mode - One life, if you die, you must restart from the last save or alternatively delete the world, it is up to you, the dev, to choose which way you implement this.
Originality - Although you've done a spactular job and I am very proud to have played this FLASH game that's better then bloody Castle Miner, a indie game, you should be proud, a FLASH game better then a group of INDIE devs. Wtf? :P
Back to my point, in all fairness, this is not original at all, it may be a remake/parody, but you, as a dev, need to incorporate something to the project and not use used idea's, perhaps make a secret level, easter eggs, extra minerals, extra smelting options, ETC.
Now, I have no experience with flash, besides what I've played, I've played lots of flash games, I had an old account in 2008 that I lost, from password and email loss so I made a new one and in all my flashy game witness, I have never witnessed a game this advanced, I wasn't even aware this was possible, so bravo.
Favourited, all my five stars and you've also got yourself a fan :D