I got an invitation a short while ago to a game designer's night at the local Snakes and Lattes (A coffee shop with 1500 board games designed to be a hangout for gamers). This sort of thing really gets me in gear working on FMB and trying to get it polished and ready to go. Obviously one of the really important things that you can do when building a game is to get it into the hands of new players and see how they play, learn and react. There will always be things that veterans think are obvious and which new players stumble over and if you can find those and polish them or add clearer rules explanations then you can drastically improve your game's broad appeal without necessarily needing to change the rules at all. This is something that old video games tended to be really bad about and which is generally improving a lot in new games. Sometimes of course you get real conflicts in design like in WOW where raiding was made drastically more accessible and catch up mechanisms were put in place to let everyone see all the raid dungeons - this is the sort of thing where you get real conflict between the people that want the game to cater to the hardcore and the people that want it to cater to the casual.
You can't please everyone. If you make your game require intense devotion of time and skill to make any progress then you end up with only the most skilled and hardcore players being willing to play while if you make it too trivial then you lose those players. There has been a decided trend in video games, particularly MMOs, towards making the entire game accessible to people who aren't especially skilled and don't necessarily have a lot of time to devote. This is a great idea from a profit perspective of course because the casual gamers outnumber the hardcore gamers by an large margin.
Sometimes though you can improve things for one side or the other without costing yourself anything. Take 4th Edition DnD for example: Abilities have keywords. A power might have the keywords Weapon, Martial, Thunder, Fear and now it is extremely easy to determine how exactly it works. No particular expertise is required to figure out whether or not someone with a bonus vs. Fear attacks gets to use their bonus in this case. Magic: The Gathering did the same sort of thing. Initially cards in the game were really randomly worded and it was tricky to figure out how many things worked. Pros spent a lot of time and effort learning all the various errata and rules about interactions and were able to use that to leverage victories while newbies continually asked "How does this work again?" Modern Magic cards are much better. The wording is extremely clear and keywords are explained so that everyone can see exactly how various card interactions are supposed to work. In both cases there is tremendous room for expertise and innovation but a new player can step in and figure out how to play much more easily than they could in the past. It is great to have depth of strategy and innovation to give the hardcore players more things to do and enjoy but it is important to let the new folks step in and know what they are doing instead of forcing them to either be clueless or spend countless hours reading errata and explanations for things that could be very simple.
FMB has all the same quandaries. How much replayability do I need? How complex do I want the strategy to be? These aren't easy questions because there are definite tradeoffs either way. I can just make the game automatically better though by making sure I always use clear language and make specific terms mean very specific things. I need to use Hit to mean a very particular thing and capitalize it so it is clear that this is a special word. I need to continually edit my sentences so that I convey all the information needed in the simplest and shortest way possible. I am sure that working on making the game simple to pick up is a much bigger factor in the game's success than the fine balance of game mechanics. Settlers has all kinds of problems in gameplay but it is easy to learn and fast to play. This has made it a massive smash success even though a game like Agricola (not at all well known) is an arguably better game from a hardcore player's perspective. Agricola takes a half hour to explain and even then the first turn is completely overwhelming for a new player - you have a tons of action choices, a zillion rules to remember and 14 unique cards in your hand which alter your strategy.
The ideal game of course fits in with Blizzard's mantra: Easy to learn, difficult to master. You need a game that can be explained in a few minutes and which has a few simple choices at the beginning but which has tremendous depth of strategy at the end. Tremendous depth of strategy can be very challenging to create but it is shocking how often it is emphasized over the relatively easy goal of making everything clear and simple whenever possible.