Focus Groups are a long standing tool of many industries. Focus Groups are good for getting an external view of a project that the developers are too personally invested in to be objective. Focus groups are also good for giving developers different cultural bias of their product which can also be enlightening.
The key to Focus Groups is assembling the groups and knowing the type of people in the group and how they align to your end goal target audience. Building all your Focus Groups from MMO fanatics that are willing to wait 5+ years after plunking down 1k cash for the privilege is going to skew your Focus Group wealthy (or wealth management poor) and no dependents (hard to pay 1k on a game when the children are hungry), this group is also going to have a very high expectation of content quantity due to play time intent. Conversely a working parent with 3 kids, at least 2 of which will play as well, is going to have a very different view of the quantity, style, and time commitment of content.
The key is to align your Primary Focus Groups with your target audience then try and adjust the features to appeal to as many focus groups without net negatively impacting your Primary Focus Group. This will give your product the largest possible market appeal without degrading your target product which will in turn give you the resources to succeed. Doing the market research to know if your target audience is large enough to support the company alone is one of the more challenging portions of development and company management.
Feedback from community forums is both useful and useless. Many people will look at the community forums to get a general idea of the health and attitude of the community as well as the health and robustness of the development team. Engaging with the community is very good as is having a few examples where you can point and say “see we incorporated your feedback, we care”. Ultimately for the health and stability of the game you will need to make decisions that many people are unhappy with for selfish reasons, it’s the problem of any GM when it is time to let the dice kill a player character. Without character death there is no risk and without risk there is no thrill.
All that being said, any idea I post is obviously solid gold and should immediately be adapted into the core game as I am obviously your primary target audience. For assistance the game features I would like released by the end of the month include: Logarithmic power growth, Item economy is based on player crafted Items made from dropped materials that exceed as dropped items, volume based inventories not slot based, Leveling and mastering crafting is time limited not raw materials limited, faction gains come from completing tasks not mass homicide, open air player markets with NPC shopping helpers, no gate or other open world teleportation only point to point transfers and many more . . . .