I don't think if slots, or dice is brainless as you think. Because before you make selection you have to think properly so as to avoid making the wrong selection, and this is still the work of the brain. so you saying that slot or dice is brainless is very wrong. Rather you can only say that slot or dice does not require strategy, I think all  gamble related activities requires brain, while most of them lack strategy.

In the aspect of being dull while playing slots games, the truth is I don't like playing slot games. So if you ask me I can't possibly give an answer to that but I have seen someone saying that he always feel dull whenever he's playing slot games.