Here’s a summary of some of the ways that Monzo delivers a superior user experience compared to the legacy banks (& apparently it’s competitors, although no direct comparisons are made).
http://www.theappbusiness.com/blog/monzo-and-the-future-of-retail-banking
I found it interesting to hear an analyst’s assessment of Monzo. For example, they point out that the Monzo widget enables you to check your balance instantly (without having to log in), something that I already take for granted.
On the other hand there’s so much praise that it reads more like a PR piece than a useful critique. Also, they end the post by pointing out yet another aggregator service (this time, built by ING) https://yolt.com/
[a] highly innovative new app marks a return to the UK retail market for an established, incumbent banking organisation. It’s also one of the first European banking apps to provide a single, integrated platform for customers to manage money across all their accounts - including those held by competitors: something that Monzo does not currently offer.
(for good reason) 
Anyway, here’s the slide deck from the post too, which contains most of the analysis -