Hero Pros and Cons
Hi Pete: I have been playing Hero for a very long time. I'll try to answer your questions at a very high level. You can get very involved and detailed thread on the Hero message board which is extremely active.
First some very quick background. I have run Hero for just about every genre. I have run multiple Fantasy Hero campaigns, several Champs campaigns, horror, science fiction, and even a time travel campaign. I'll warn you that Hero is my favorite game system. Part of the reason is my familiarity with it.

Keep reading.
First the good stuff...
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Hero is extremely flexible. Not only can you build every genre under the sun with the same set of rules there is often more than one way to purchase the same effect. Hero is a point based system that use a concept called a "special effect" to make the system general and flexible as all get out. For example, there is a power called Energy Blast. It can be used to represent Cyclops eye beams, a fireball spell, or an alien laser pistol. VERY powerful. This is extremely powerful for fantasy genre magic systems. You can actually craft a complete magic system in Hero that differs from every other Fantasy Hero game.
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Point based character creation is cool. This allows each player to create the character they want but keep all characters at relatively the same starting power level. There are no class buckets at all. If you want a mage who can lift his horse you could do that...well...if you had the points. Some of the points are gained from disadvantages. This concept is VERY cool. It allows each character to have individual hangups and such. Maybe they are hunted by a scorned lover and have an intense hatred of orcs. The system easily handles it.
Now some bad things...
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The system is hard to learn initially. Often this can make it feel unapproachable. Hero is trying to help by releasing products like SideKick which are scaled back versions of the full 380 page rulebook. I personally don't feel they scaled it back enough but this is a matter of opinion. If you want to try it find a Hero GM and play a couple of sessions. See what you think.
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Hero is difficult to GM as it requires lots of work initially. This is the back edge of the flexibility sword. For Fantasy Hero, a GM would have to establish a magic system, work on campaign guidelines, create monsters, etc. Granted there are support books but as everything is so customized sometimes they are not as helpful as you might think.
Some general thoughts...
In some ways Hero is kinda like Home Depot or Home Club. Once you learn the rules you can walk in and pick raw materials off the shelf to build the effect you want. It may take some time to build that house from the raw materials but it is certainly possible. The trick is that you have to know the tools but once you learn them you can build anything!
I consider D20 more like buying from a boutique store. You can pull the fantasy module of the shelf and start right away...but it may not be easy to build a science fiction game unless you also buy the module for that genre.
Hope this helps.
