Full of questions.Follow

Steam does the same thing with some games (almost).

It'll say "+x hidden achievements" but it won't tell you what those achievements ARE until you've earned them (to avoid spoilers usually).

FFXIV, as noted above, doesn't even do that, it won't tell you how many limited time achievements you're missing. You'll just have a slightly lower achievement "score" than someone who has done a few of them. Not that anybody I've ever met actually cares about the score. And even then, most achievements only give 5 points except for a few. So if you're missing, say, 30-40 points... meh. Whatever.