AbdulAlhazred
Legend
One other thing I would add on 4e SCs. There are 5 complexity levels, each requiring more successes. Yes CL5 is harder than CL1, but let us look closer... Typically a party of 5 PCs will cover 80% of the skills at +5 or better, yielding around 90% success rates per check. CL1 requires 4 successes. So, your chance of outright failure is pretty low. In the first 3 checks it's like 0.1% and only 1% of the time you will stand at 2 fails at this point, so you have pretty close to a 99.9% chance to either succeed at check 4 or go on to 5. Overall success rate here is pretty close to 99%. The GM gets a hard DC, and the fiction could box the players into a suboptimal check now and then. So we might conclude that the easiest CL1 is at least a 90% chance of success, probably more like 99%.
Now CL2-5 ARE harder, but each additional check doesn't increase failure rate much, because characters just don't fail checks often! Players can also expend resources like powers, consumables, etc. These expenditures usually grant success, or at least move the DC down to easy. So even CL5 is probably only failing 5% or so of the time.
But that is fine. How often do parties get their clocks cleaned in combat? Not often in D&D unless they are totally reckless. You can be reckless in SC too. If your fail chance per check is 25%, CL5 is pretty much certain failure!
My point is, the players are much more in charge of how hard things are than it might seem. The GM can certainly throw curves at you, but I would not call the difficulty arbitrary. No more so than with combat that falls within the encounter guidelines.
Now CL2-5 ARE harder, but each additional check doesn't increase failure rate much, because characters just don't fail checks often! Players can also expend resources like powers, consumables, etc. These expenditures usually grant success, or at least move the DC down to easy. So even CL5 is probably only failing 5% or so of the time.
But that is fine. How often do parties get their clocks cleaned in combat? Not often in D&D unless they are totally reckless. You can be reckless in SC too. If your fail chance per check is 25%, CL5 is pretty much certain failure!
My point is, the players are much more in charge of how hard things are than it might seem. The GM can certainly throw curves at you, but I would not call the difficulty arbitrary. No more so than with combat that falls within the encounter guidelines.