A simple example is that here I sit in Hong Kong, and my upcoming flight from San Francisco to Melbourne (which departs at 00:50 PDT) is showing as departing at 17:50 HKT, which is true but useless. That's the hallmark of a system designed with the data structures in mind first. With (too many) clicks I can change it to display in PST, but now my diary for today in Hong Kong is wrongly displayed.
To some extent this is a flaw in iCalendar's data model, but it's not insoluble, if you start with the right perspective i.e. user stories. So my general complaint is that this kind of "data first" rather than "utility first" design pervades the Google Calendar application.
(Don't even get me started on the "world clock" extension, it's just garbage).
Judging by the listing of optional extensions in the "Labs" section, Google Calendar has languished with little serious development since 2009. The main utility to me these days is that it can aggregate multiple calendars, including subscriptions to external feeds, and then pass on that aggregation to mobile clients.
So I think it's another dying Google product, one that was misconceived in the first place, and I too am interested in alternatives. However calendaring is hard and none of the alternatives I've considered to date were actually better; all limited or flawed in other showstopping ways. So Google Calendar remains the least crap of my options.