blargney the second said:
1) Tightly themed PCs whose range of abilities doesn't diversify significantly over the course of the campaign.
Something not class/level based, probably. I have a lot of love for d20-based systems but the truth is that every time a character goes up in level they get access to all sorts of new goodies to make them more diverse.
2) Less death-centric than D&D - I want PCs and NPCs to survive.
SW-style wound vitality actually results in high rates of mook survival. Mook takes a couple points of wound damage, fails a save, falls unconcious and is (hopefully) not coup de graced by the pcs. Other options are True20 style toughness or just having a crap-ton of hp ala Iron heroes. Unfortunately I don't know of any classless systems that have high survival rates, besides Exalted and that's really only for PC survival; Exalted mooks die by the thousands.
3) PCs that have the ability to keep adventuring all day long. Abilities usable as many times as they need, and fairly quick recovery times.
True20 and Iron Heroes will both give you this.
4) Fast-paced, straightforward, and exciting combat. No effects that require 5 minutes to resolve.
Unfortunately this one is difficult. Exciting combats tend to also be complex combats because someone is doing something cool that requires some extra adjudication. On the other hand, combats that are quick tend to be dull.
Some conclusions:
I'm a big fan of Iron Heroes but it can be clunky at times, especially when everyone is just learning the system. Once you get a little practice in the only clunky mechanic becomes grappling, which is always akward in d20 games. As mentioned previously, it will also require the least amount of conversion outside of the PCs.
True20 is a fine system, and for me it works wonderfully for certain game types but while I like it a lot I would never use it with Eberron. It just wouldn't feel right to me and it's a good bit more restrictive than I desire, especially when it comes to skills.
You may want to take a look at Gun-Fu and try adapting it to your Eberron games. The mechanics are similar to those in True20, but adapted to make sessions more like a Chow Yun Fat movie. Their actions per round is interesting, even if you don't like anything else from the system. "A character may do as much in one round as can be described in a simple sentence, such as 'I jump over the machinery and come down, guns blazing, upon the five guys on the other side of it.'"
If you're willing to take a big leap, you may want to look at the Exalted system. Strip out the demi-god flavor and remove some of the more outlandish abilities and you might have something you'll enjoy playing. Also it will let you have hideously powerful opposition whenever you wish by using those rules that you've forbidden your PCs from using.