You could say that about any first in a series game?.. Halo 1 was almost an open world game with a cool eco system of wacky creatures along side covenant outposts. Minimal voice acting too.
Your comment implies that all we're going to get from this universe is AH1. Mundfish are planning to release 2 more DLCs after this one, and a sequel is already being planned out (some kind of 'military bots' are supposedly going to be a new enemy in AH2).