I think Nemesis was undone by some poor decisions but by and large I don't think it was that bad. For what it's worth, my favorite TNG film is Insurrection precisely BECAUSE it felt like a TNG episode.
The DW 50th anniversary, like anything, will delight some, piss off others (though the ones that will be pissed off are the fans that want to act like 1981 was the paragon of Who and everything post-2005 sucks) and leave others ambivalent. There's no way that it can match the hype. But I will say that even I have this weird feeling about it, like they haven't done as much as they could have to take advantage of this opportunity and will try to cover it using "sight cameos."
Of course, that could all be part of the misdirection. Who knows? They might have a load of surprises in there that no one expects.