Kraken has been around for a while, I've never had a chance to complain about them even though its been a while since I used their services but feedbacks are not to be joked with.
If multiple people have complained about their accounts and their complaints aren't subject to a particular thing then I suggest the reviews have to be taken seriously by users, but if the complaint borders around a particular reason then chances are, they are yet to get it right or maybe they are from the same region and they have some restrictions.
From what MAAManda said in his post above, he only found few comments about unwilling closed accounts fortunately. So it doesn't seem to be a very widespread practice if he is right. In the two comments he mentioned only one of them complaining about not returned funds and it was "only" one week after the closure. So they don't seem to scam people like dubious exchanges and casinos, and to stay rather professional despite some complaints.