In all honesty, most brainstorming meetings are excruciating at first. After a while, depending on who you're working with and the flow of the conversation, you can start building some momentum. However it feels like it takes an hour to accomplish 20-30 minutes worth of work.
Some of the most effective brainstorming sessions that I've been part of are ones with some sort of structure in place. Not structured to the point of stifling any creative process. Just structured in such a way that the meeting is being held in order to accomplish something, not sit around awkwardly.
I recently ran across this idea via Harvard Business Review called "brainswarming." Sure, the name lends itself well to eventually becoming a buzzword but the idea behind it makes a lot of sense. It's a goal-oriented way to solve a problem by combining ideas or thoughts that may not have been thought of before as possibilities.
The video is a very short watch and worth it. I think I'm going to try this at my next brainstorming session. Curious to see what thoughts everyone else has on this tactic too.