A huge number of people put massive stock in graphics. For that group, playing something they already liked with better graphics is a fantasy come true.

A second group that helps make these popular is the crowd that didn't get started gaming early enough to catch the first release or even own consoles that can easily play them. For that crew they're seeing a good game for the first time and...yeah, of course they like it. Deadspace is a great example, there are a BIG chunk of gamers out there that weren't able to play a horror game 13 years ago and it's a legend, of course there would be interest in getting to play it now across teens, 20-somethings and older folks who missed it the first time around and the updated graphics just make it all the more appealing.

Mix those together and a fair chunk of people will buy it.

Now, I need to add another item here: Most "professional" video games reviews that are heaping praise on these are done by various media outlets which depend HEAVILY on video game advertisements for their revenue. Whatever the big sales push is from a developer, it's going to be well reviewed by all those outlets. If it isn't, they're not going to keep getting ad revenue for long. It's the same reason car and driver basically virtually never gives a bad test drive review, whatever industry you want to pick.