Computercraft is a mod for minecraft which adds a computer where you can create programs for minecraft and one program lets you play a text adventure game where you mine ore,craft items and other things by entering a command. Would you play a game similer to this as a stand alone game? Do you have any ideas of commands that should be included?

It depends. The whole point of text-based games is that instead of having a powerful GPU display the world before your eyes, you are simply told what you see broadly and let your imagination do the rest. It probably wouldn't work well if you stick to Minecraft gameplay, since your imagination will not have a high enough accuracy to achieve anything. The idea is of course that if you aren't completely braindead your imagination can produce a setting infinitely more realistic than anything a computer could display.

That said if the game is something like:
"You wake up in a forest. To your left, a stream reveals the presence of coal shimmering under the water. To your right, you can see a mountain covered with age-old conifers in the far distance."
I would probably give it a go, not so much for the gameplay but just for fun. Such games can be extremely relaxing and quite impressive if done right.

That's actually a pretty cool idea - have the computer run a blocky, low-resolution simulation of the world, minecraft-like, and let the user navigate through the world through a text-based interface. I would definitely give it a shot. The advantage is of course, if you are willing to throw away the graphics, you can fully concentrate on the underlying simulation and convey it to the user through some well-written text. The simulation doesn't need to be perfect since the human will take in the low-detail simulation via the text interface and fill in the gaps itself via imagination. As long as the computer simulation and what the human interprets from the text stay coherent, it should work.

Commands: walk - n/s/e/w up/down, look, mine, take, examine, open, craft, use item/weapon, place, drop, eat, drink, sleep, etc., etc. You need to solve riddles in usual infocom manner, but you need to survive to mine as well as create the needed stuff to get the princess or something.

Sample transcript:[spoiler]
> LOOK
Mine
You are in a maze of twisty little passages, all alike.
> N
It is pitch black. You are likely to be eaten by a grue.
> I
You are carrying:
A worn brass lantern (turned off)
A broken wooden pick-axe
231 blocks of Wood
10 blocks of Stone
2 blocks of Coal
> TURN ON LAMP
Done.
The lantern comes to life, though the flame is getting fainter. You are holding the lantern.
> LOOK
Mine
You are in a maze of twisty little passages, all alike. On the cave wall where hangs a strangely familiar looking sign. "BEWARE THE ZOMBIES!", it reads. On the ground is an elven sword. It is glowing faintly blue.
> TAKE SWORD
While bending to take the sword, you accidentally drop your lantern. It falls to the ground with a crashing sound.
You are now holding the sword. It is suddenly glowing quite strongly.
A zombie appears, give you a strange look, then attacks!
> KILL ZOMBIE
What do you wan't to kill the zombie with?
> SWORD
You miss. The zombie takes a swing that catches you completely unaware.
*critical hit: you take 30 damage*
Your head is taken clean off. Remember to bring more life potions next time.
***You have died***
[/spoiler]