Slight (DC 13): a score of 2. This is no problem whatsoever. Assuming you have a Dex of 16, your score should be +7 with one rank, and you can succeed at a 6+, which is 75%. This seems right in line with what I want to see.
In fact, this is the DC for two slight difficulties.
Now, those numbers are assuming no synergy bonuses (I thought you said you were getting rid of them), and no bullshit bonuses from popping some quick psionic trinket or something. I'm just looking at base ranks and roughly what I'd expect from a Dex score at those levels.
Well, I'm not sure if I'm going to use synergy bonuses or not just yet. I might. Another thing to remember is that as you gain ranks and the ability to navigate extremely or impossibly difficult terrain the DCs for the others go down. Like at 7 ranks, you can navigate extremely difficult terrain, you ignore slight difficulties entirely, and the DCs are bumped down for everything accordingly. So at 7 ranks a moderate difficulty goes from being DC 18 to DC 10, two moderates goes from DC 23 to DC 13, one severe goes from DC 25 to DC 18, one extreme is now DC 25, two extremes is now DC 35.
Perhaps you should stack them differently. You could always follow the simple DMG guidelines of +2 for every factor, starting with a base DC of the hardest thing.
Possible, I suppose, but then there's no distinguishing in difficulty between scattered gravel and three feet of snow or between walking a tight-wire and walking along an 8 inch wide path.
Actually, one very very basic use of Athletics.
Increase movement speed.
I like this idea very much.
I'd suggest granting some precision damage stuff to the Heal skill. Either you gain minor sneak attack, or your damage dice increase in size, or you get to reroll them. Possibly a DC boost to effects like Stunning Fist, coup de grace, and poisons you craft as well.
Would be nice if certain types of wound needed Heal checks in addition to magic to fix (the idea being that magic is "dumb" and can't do precise work by itself). Maybe such wounds could use mechanics similar to diseases.
Yeah, I've trying to come up with a way to re-incorporate Heal. A Biology skill might work if it covered as much area as the Arcana skill, in it's given field that is.
I know I am a little late to the party but on the Save or Die/Suck stuff if you had a mechanic to deal with them it would be good....
Possibly something along the lines of Toughness points:
I'm going to attempt to reduce the effectiveness of save or dies and save or suck, yes, but I think it will be more in the department of giving players better defenses against them rather than nerfing them into uselessness. I'm leaning toward using a lot of 4e's status ailments, which are generally milder, and shrugging status ailments off should be much, MUCH easier than it is for characters.
Save or dies will be rare, but when random player death rears its ugly head I hope to provide mechanics such that death can really be "just another adventure."