It's definitely challenging, but there's a certain sense of progression so I really didn't feel that the experience was THAT tense. I mean, bosses have different phases, and each time you try it you can see how your skills improve, and you know the boss patterns' better. I guess that people who freak out like in the video might have the opposite experience. If you feel angry, you tend to play worse I think.

Also, I forgot to mention that the game has a "kind of" easy mode. You can't advance playing the bosses in this mode, but it works for learning how to beat the bosses. Don't be scared about the game if you feel like you might enjoy it, it's not that bad as some people might... suggest.