Blockz game - How to improve the level of difficulty

[arj0n]

I've been working again on my game Blockz since a few weeks, it now contains 75 levels and it's graphical design has been modified.
The only level of difficulty the game now have is the limited numbers of moves per level.
I removed the time-restriction because some people said that a time limit is/can be annoying.

Q:
I wish I could implement/use something that makes the game harder and harder to beat once you finished more and more levels,
but with only having the limited numbers of moves, the level of difficulty is pretty 'linear' throughout the whole game...
Or is the limited numbers of moves per level enough as difficulty level?
Any ideas?

[cat]

You could give each level a name/id, let testers play the levels in random order and rate them for difficulty, and then sort the levels by average difficulty. It's not always the number of moves, sometimes it's how obvious the moves are.

Great you are working again on that, I did like the demo!

[Ghost]

What cat said; quite often a level can't just be rated as difficult because some players will find them obvious and others will fail to see the solution- this needs a large tester pool.

You could also introduce the somewhat casual method and give "gold, silver, bronze" rankings: If a level has a perfect solution of five moves, make that trigger a gold ranking. Seven to eight moves, silver, everything else bronze.
This doesn't add difficulty to the level but gives players who pass a level some motivation to try it again until they score gold.
I hear it's become common that the programmers even include platin for players who manage to beat the already perfect solution; there's always someone "more clever than you".

And heck, cool BLOCKZ is back! 75 levels sounds pretty awesome too- level editor?