This may be the most important! :) Even though I have guidelines, I don't always follow them when it's better not to (to preserve the "flavor" or "feel" of a character).
Also, I'm constantly adjusting, based on actually playing the game. In the end, having a character "play" like his comic book counterpart is the most important, and just using math formulas doesn't always get you there.
I started out trying to set hard and fast rules like "Strength 5 equals x tons, etc.", but found that it made all uber-heroes have 10 strength and hardly anyone in the middle. Instead, I've adopted a "relativity" system.
We all know who the strongest and fastest heroes in the universe are (more or less!), we also know who's not so strong and fast. So, when creating heroes, compare them to others. ("this guy's as strong as Superman, but slower than Hulk, etc.") This leads to a nicely balanced set of heroes to play with or against and is one of the guiding principles of my site, where I even compare them to Freedom Force heroes.
This is a great way to simulate fatigue in your heroes. It also keeps some heroes from being unstoppable melee machines (which isn't much fun to play with or against). Finally, it lowers the overall prestige point cost for your character.
Of course, this also means you shouldn't give all your characters 10 Energy so they never get tired. :) Let players "pace themselves" to win. Hmmm, strategy...what a concept!
There's really no need to create 5 different attacks with cool names that are basically the same (i.e. "Punch", "Nasty Punch", "Really Nasty Punch"). Why would you ever use one over the other? The "overpower" feature lets you adjust the damage you're trying to do, so damage shouldn't force you to do this.
For example, if you have a hero who is going to have both a normal punch and multi-hit attack, give him a reason to use the punch. I usually make the multi-hit attack a bit slower, make it do less damage, and make it cost more energy. This keeps it from being abused and makes it a bit more "unique". Maybe that kick could do knockback damage but the punch does stun damage. Mix it up a bit.
In fact, try to keep every power "unique" somehow. For example, I don't need Blue Bowman to have both a "Net Arrow" and a "Glue Arrow", since they both do the same thing (Stasis).
I generally try to avoid having Passive Defenses for heroes. I find it's really no fun to play against anyone where just about everything I throw at them comes back with a "Blocked" or "Resisted" message. Instead I give them Active Defenses when it makes sense (a forcefield). Or make use of Material Type and attributes like Armored or Volcanic.
I will use passive defenses if a character really should have an "Invulnerability"-type power. However, in these cases, I still never go over 50% chance of resisting and I seldom let it block "Direct" attacks. I also try to include a "weakness" where possible.
Since Freedom Force has the great feature of letting you "overpower" your attacks (by right clicking on a power), I rarely set damage on melee attacks higher than Medium. Remember, the Strength of a hero will be used to calculate damage done anyway, so setting damage to Extreme for someone with 10 Strength is where those ugly 150+ point punches come from.
It's more fun to have the game last a while, with you hero having to land a few blows to take out his foe. I am even considering going to "Low" as my default to make games last a bit longer.
As I mentioned before, I try to use attributes as much as possible. Some of them have strange or misleading names, but they are still exactly what you're looking for. Read the descriptions!
Updated July 6, 2002: A good observation by the Unbeatable Silencer:
"Similar technique can be applied with respect to a character's Material. For example, when creating a Wonderman-type character, who (according to Marvel) has resistances to all types of attacks except Mystic and Psionics, you may want to use Stone as the material in combination with Strange Visitor and Neutralize. This makes you Resistant to every type of attack except Mystic and Mental. If you can't live with being Highly Resistant to Piercing, use Thin Skinned attribute to offset it. Round off your Wonderman by giving him an Almost Always defense vs. Cold and Fire. This methodology is cheaper (points-wise) and much more realistic than creating an uber-passive defense."
Thanks, Silencer! To help you all if you want to do more with the Material setting, I have put together a reference chart on the various Materials. Click here to see it.
Yes, "Stun" is a part of comics. However, you don't see Spidey stunning Venom every time he hits him. That would get pretty silly (and boring). In game terms, it's no different. I try to keep the Stun setting at "Low" when I use it, especially on melee attacks.
"Knockback" is a bit less cheesy, but again, it's not sporting to punch someone for 5 points of damage and watch them die as they go flying for another 80 pts. I usually only give Knockback to people with immense strength or martial-artists types.
Plain and simple, I don't use the Heroic, Extra Heroic, and Unheroic attributes. Why? Because I think they give heroes with them a distinct advantage (or disadvantage) that borders on cheese. I think one hero point for everyone is plenty.
Besides, if you were reading a story where HyperGuy "uses a hero point" to overcome injuries, etc and keep fighting, wouldn't it seem really lame to have him overcome a bunch of more injuries a couple of pages later? Once is plenty.
I think it's safe to say we all have favorite heroes. I also think it's safe to say that we are all guilty of "tweaking" them a bit to make them a little better. ("Well... everyone knows Ninja-Guy's real scary, so I've given him a Panic beam power with very high accuracy"). I tend to think that if they're not "real" powers, it shouldn't be used. Again, there are always exceptions, but how silly would it be for Ninja-Guy to scare Cosmic Overlord Villain away with his panic beam power?
Some heroes rely on gadgets which have to be built as individual "powers". This makes their costs quickly escalate to where they are comparable to heroes with much better stats or powerful attacks. It just goes to show that overall cost is not always the last word on who is the better hero.
The answer? Absolutely nothing. Nothing is special about 10K as a limit for heroes. In fact, it's not really a set limit I try to work towards. Instead, I find that by sticking to the guidelines above, most of my heroes end up well under 10K all by themselves (a few powerhouses end up slightly over). I never go out of my way to make this guy cost 2,000 points more or 1,000 points less.
It is also worth noting that the Freedom Force heroes all also "fit" in this type of scale. I am sure Irrational Games designed their heroes with balance and fun in mind, so that should tell you something (and nobody has more experience hero-building than Irrational!)