I had hoped to finish this last year, but ran out of time. Haven’t done much in the past 6 months - I’m working on level 4 at the moment.
http://www.cheddarmonk.org/java4k/shift4k/
Update: submitted with version 1.0.
I couldn’t even get past the second level, where you have to fall back and forth between 3 spikes. Or maybe I went the wrong way.
I actually got to the bouncing around in Level 2, but I missed one bounce, and I died! Nothing wrong with that, I guess, but I had to start all over 
Checkpoints (where you begin after you die) would be an awesome addition.
I’m also floundering on Level 2. I think the BONUS is safe ;D
I got to level 3 but couldn’t get past the white arrow on the left. I died when I tried to jump because of the spike. Don’t see how to pass that part.
I would add checkpoint too.
No, up to that point it forces you to go one way.
Ok, I knew it was a hard curve but it seems that it’s too hard. (Alan, you should see how nasty the N is!) Maybe I should move the current level 2 to 3, 3 to 4, and insert an easier level 2. Probably convenient for me, because level design with this mechanic is really quite hard - far harder than previous puzzle games I’ve designed levels for.
I shall think about checkpoints. I think I can squeeze them in, but I’ll need to come up with some graphics and probably change the tile representation (I think I allocated 3 bits for the tile type and am using all 8 possibilities already).
Hey, this is really cool. You’ve managed a neat implementation of shift in 4k - good job. 
(I completed level 2 without taking the ‘O’, which was quite difficult enough for me, heh.)
New version uploaded. I’ve inserted a new level 2, added a draft level 5 (got some empty gaps it would be nice to use), and added some checkpoints from level 3. With the addition of checkpoints it’s now much easier to get the hardest bonus letter.
Level 2 owns me.
I think I’m going to need to watch some people play this to see what they find difficult.
Ok, I got it. I think it would be better to introduce concepts more slowly. Level 2 has a ton of stuff on it, it is daunting. My brain has a lot of trouble trying to figure out what is going to happen when I shift. I mostly just walk around and try shifts at various places.
I got past level 3. Whew! My head hurts! 
Really cool game, BTW!
Brilliant implementation of an inspired game.
I stopped playing on level 4, I died and didn’t bother continuing.
Me too, but an uncompressed level is 402 bytes. And I’d have to add extra code for the bonus letters. Maybe it can be done, but until I have level 6 in the game I’m not sure how much space I’ll have. Most likely I’ll try to add a bit of explanatory text in-game.
(There is also the thing that it’s based on a series of 4 games, which I think are reasonably well-known. I’d rather send people who don’t know them to play the original Shift and Shift 2 at Kongregate or ArmorGames and then come back than bore people who do know them by using half my levels on tutorial).
Oh right, I wasn’t paying attention that it was 4k. All the more impressive!
Wow! Only just got around to looking. What a brilliantly original idea. Bloody hard though! A very cerebral experience.
Cas
I’ve submitted. The pack.gz still has almost 400 bytes spare, but I’m not going to have time to add anything else, much as I’d like a nice squelchy death sound effect.
I was able to get through 5 levels easily, but without getting the bonuses. The bonuses are much harder.
Good: that’s the idea.
FYI your game doesn’t work on OS X at the moment. See this thread for a possible fix: http://www.java-gaming.org/index.php/topic,23434.0.html