invenio: I don't think the URU games are bad, but I think it did take the series in a completely different direction. The "original" myst series focused on one family, while URU is more background story about the world itself. This is not bad, but I just found that I got a closer attachment with the characters in the first series of myst games. Also, I like the pre-rendered style of the game better than realtime 3D. Riven simply looks better than the last URU game released. This of course is just my opinion and personal feeling on the matter. I'm sure others will disagree and that's cool.
Absolutely, URU and EoA have a much broader scope than the other games in the series that, like you mentioned, focus mainly on Atrus' family. For me however the story conveyed trough Atrus' family was always at its heart a story about the downfall of a civilization, about the D'ni, about the Art and its implications and without URU and EoA, mostly URU, it's an ambivalent, incomplete and unfulfilled story. I understand that moving away from the more intimate focus of the other games may not have pleased everybody but, for me, URU is the one that tells most of the true story, both (relatively) recent and ancient.
As a game Riven is definitely my favourite though, no argument there ;)