I was watching this video:
 
 

I always thought how good you were at a game was mostly down to how long you played it (not including high level tournament play). My friends have always increased in skill at roughly the same rate.

But then i saw Brad play and had to reconsider. 

it depends if you are making a game like Bioshock the answer is no, the good elements of that game were not taken from games.Bioshock could have been designed by someone who had never played a game. If you are making a SHMUP or bullet hell game, then you have to be awesome at them because your audience is incredibly discerning.

As a game designer, I can tell you that no, you don't need to be "good at games" to design games, but you need to have an understanding of what makes a game fun, what challenge level is too light or too hard, and so on. While I would consider myself a fairly good player in most genres, I sometimes have to rely on the feedback of much better players in order to get a good idea of how fun the game is for them. Thankfully, my office is full of players of different levels, so we can get feedback from newbies to pro material.
 
Working with one game and designing it feature after feature, you naturally get a decent understanding of the mechanics and you will usually become pretty good at it in the end =) Still, judging from the video in the original post, that seems to require some smooth handling of the gamepad, which is a skill that even the brightest designer might never achieve.

I think you have to know what makes a game good, but you don't have to be good at them.

Depends on your department. If your working on the gameplay then I'd have to say yeah you need a certain amount of skill to know what will challenge good players and what will appeal to players. If you're doing art assets or animation or something else like that then I don't think it's very important.

I don't believe you need to be "good" at games, as it mainly boils down to figuring out what makes games "tick" and then using these features, as well as your own, to make a great game.  I've known and spoken to devs who've said that a lot of devs hardly even play games (apart from the ones they're developing).

"

You could be the most terrible video game player there is but be the most brilliant video game designer if you know how to make a game. There's a difference between being good at a game and making a game. 

 Ignore the indent. Won't let me decrease it. "

Well if the developer can't play and understand his own game you could get horrible game balancing in a game like season 5 WoW arena. 
 
But mostly naw, the developer just needs to understand what people like and enjoy to play to make a good game.

Probally not, itagaki makes difficult games yet he plays like a total noob.

Might just be me, but it seems like the developers never play their own games well when they showcase it.