It is criticism and it is constructive, which is a good thing, but I'm still not sure.
AquaMail actually showing event details ("text") -- without having to click "expand" or "show details" -- bad thing?
Accept / Maybe / Decline buttons -- make color-coded?
AquaMail indicating that you've already "accepted" (in your screenshot), by disabling the button -- also bad?
How would it work with color coded buttons? Would it be obvious when such button (non-standard appearance) is disabled?
Being able to add a note with your response -- which requires a checkbox -- also bad? Remove the checkbox, replace with an "note" icon -- "what's that little thing there"?
More graphics, more vibrant colors, replace a standard button for "view" with an touch-sensitive image that doesn't look like a button?
To me, this other app make a great first impression, it is "inspired by modern magazine design" or whatever it's called, but is it easier to understand and more usable?