A change... But a sorely needed one. Imo, one of the biggest problems with Halo was how linear each one was. Such little to explore for such a lore rich universe. The change to an openworld environment makes exploration a much bigger part to play. You no longer have to always engage enemies to progress, finding collectibles actually benefits you in-game (did I mention you now have unlockables and upgrades?), and thankfully finding UNSC weapons is not as difficult this time around.
Have not beaten the game yet, but so far I am very much enjoying this refreshing new adventure with 117.