How can I ensure the Commander deck I'm creating is appropriate for my group's meta?
If there's one thing you can learn from Mark Rosewater's "Making Magic" articles (check out the section on "Empires"), it's that the best way to find out if a deck is unfair and/or miserable is to play it. This may seem like something you could shortcut, but card evaluation is really hard, and cards or decks that seem oppressive at first glance may turn out to be actually really fun and exciting; and vice versa.

The key thing here is to have a group happy to communicate that your deck is stopping them having fun, and to be able to tell which deck it is that's doing it. The best way to tell this is the same way you'd analyse anything; change one thing and see what happens.

For example, if everyone turns up with a new deck, and one can't compete, one's horrifically broken, and one just feels like it could be fair if the removal suite in the opposing decks were different, you change the broken one, and see how it fits. If you change all of them, suddenly you could get massive swings against the "could be fair" which you weren't expecting.

Also, be aware that if your deck is requiring people to significantly adapt their decks to deal with it, then even though it seems fair, it's actually warping.

Another issue is play skill; for example, Black Lotus is an entirely reasonable card as long as you're using it to ramp into Centaur Courser on turn 1. The deck may seem reasonable, and then suddenly stop being reasonable in the hands of a more experienced player. So it's worth agreeing that, just because a deck was fine originally, it could now be time to retire it as it starts to cause issues.