I just started playing Sacrifice last night, and man what an awesome effort this mod represents!
It had been quite a while since I had played Aquaria, having done one thorough completion and then more recently one speed completion; doing a thorough run first up (including a little help from walkthroughs) meant motivation was somewhat low for playing through again. But this is a whole new ballgame, and fully brings back the wonder of discovery that the base game had to start with. Well done!
Really enjoying the conversation system and well believable characters and personalities for the most part, with Old Fred and co for some comic relief.
As for some of the recent discussion re difficulty, I have found it to be pretty well balanced so far – not sure if that was for an older version, but I don't think save crystals are too common, and with all the conversations taking time and such I find there is extra motivation to get things saved. The currency system is interesting and it was fun to see some out-of-water action quite early on in the piece.
I had to stop myself playing around midnight, but am looking forward to getting back to it. All I've really noticed that might be good for an update is typos - "You have no large crystals to ex(c)hange"; and Naija says "Your right" at one point. Not being able to look at the map is really hard to get used to; it's a shame that that's just how it is.
Edit: BTW this was all on a MacBook Pro early 2008 running OS X 10.6.1, and I haven't had a crash yet. The only buggy thing I did notice was the first time I've seen that old bug where the saved game preview picture becomes just a blur; for both base game and Sacrifice saves.