Totally useless, a totally generic email. I'm among the people who do not believe a "we'll get better" message when it does not mention any specific measure explaining how, and I find it almost insulting that they would hope I would believe them when problems keep occurring/reoccurring with similar causes producing similar effects.

I would have welcome a "we realise this was unacceptable but here is how we will ensure it won't happen again" email, but a "we realise this was unacceptable and sort of hope it won't happen again" message does not tell me anything useful (and I was affected, but not nearly as badly as others as in my case, it only resulted in a delay and I still arrived the same day).