It's a good game, but I probably wouldn't bust $120 on it.  Having it new in box is great for me because I know that way the manual isn't all wrinkled and creased up and I can keep it in good condition.  But I wouldn't be buying as a collector just to shelve it, I would open it.  So I bet you could get a loose one or a used for a lot cheaper if you looked around.  Ebay has a couple, about half of that for a loose one, but you could get the PC Engine release there looking complete for $35.