I hate to be one of the "underwhelmed" few, but I think I will stick with my NGH. I played the Japanese MS3 version over at a friends house. I do not know, I just wasn't impressed. Granted, I hate Metal Slug 3, but still...
It is kinda the same way I feel about The Last Blade 2 import. It is fun, it has blood, and looks like the NGCD version at least, but meh, it is just not the Neo.
I think, like someone else said, the aesthetics are part of it. There is just something about poping that huge cart into your system, no load times, and playing with an old style stick. Nothing like it.