The N7: How can anyone call themselves a gamer if they haven't experienced Mario, Zelda, Metroid etc. !? Day 1 buy.
PS4: While I would like to buy this day 1, I will probably wait a year since it will be quite expensive up front and the games won't be there at the start. This is a definite buy though.
Xbox720: Maybe the toughest one to justify for myself. I will only get this at launch if it offers cutting edge gaming at a reasonable price AND there isn't much on offer from Sony or Ninty at that point. Most probably I will buy the console after a few years, but the possibility of skipping it is also there. Especially if my buddies have one and there's only a handful of games that make it worthwhile.
In any case, I will probably (again) buy everything on the market at some point. I just love games too much not to.
