Planning on buying an Xbox One.

[Azzanation]

If you want good value and quality, than id say pick up Rares Replay, thats one of the best collections of games ever created plus Halo MCC, which offer the best Best versions of all the Halo games that will keep you busy for months alone.
Those two games offer you a total of 35+ games that will cost you as much as one full priced game. Not a bad way to build up your X1 library.