They were generally considered unsavoury. Here are three references:

In Warwijck's 1598 journal (Rothschild, Walter (1907). Extinct Birds. London: Hutchinson & Co.), describes the bird as follows:

These we used to call 'Walghvogel', for the reason that the longer and oftener they were cooked, the less soft and more insipid eating they became

Herbert in A Relation of Some Yeares Travaille into Afrique and the Greater Asia from 1634:

the Dodo, which for shape and rareness may antagonize the Phoenix of Arabia: her body is round and fat, few weigh less than fifty pound. It is reputed more for wonder than for food, greasie stomackes may seeke after them, but to the delicate they are offensive and of no nourishment.

In the journal of François Cauche from 1651 (Strickland, Hugh Edwin; Melville, A. G. (1848). The Dodo and Its Kindred) it says:

It has a cry like a gosling, and is by no means so savoury to eat as the Flamingos and Ducks of which we have just spoken.

I also found this contemporary Dutch account from 1598 but at the moment cant find the original source:

finding in this place great quantity of foules twise as bigge as swans, which they called Walghstocks or Wallowbirdes... But finding also aboundance of pidgeons & popiniayes, they disdained any more to eat of those great foules, calling them (as before) Wallowbirds, that is to say, lothsome or fulsome birdes*."*