My first reaction to this is: great! It might be a tad late, but hey, better late than never. Just because it might be easier to download a free emulator and get hold of some ROM's, this is not what your average PC-user will do (because they probably don't know how to do it). Besides, what they offer sounds like a really good deal, and if they manage to deliver quality I see nothing strange with subscribing, even though the free emulator & roms are just a couple of mouseclicks away.
I do hope that the emulator which will be used will be able to run in 60Hz VSynced mode (or 120Hz vsynced mode) so that no glitches will occur. Otherwise I will bash it indefinitely... because it is not possible to get accurate screen updates if being run in, say, 85Hz... either they will have to deal with frameskipping or framedoubling or just let the whole thing run too fast... which I simply can't stand.
Also, I've seen some horrible examples of commercial emulators and their services released in Japan, in the same style as these services will work (can't think of the names, at the moment) and what they offered was no full-screen, horrible aspect ratio on the graphics and absolutely no vsync whatsoever. My thought was... is this a joke?
Not even the GameboyPlayer released for the GameCube here in Europe managed to offer a solid experience... the screen update will jerk around at regular intervals, rendering the gameplay horrible if one is as picky concerning these things as I am. I never bought it thanks to this.
I am a bit scared. Obviously. Will they manage?