I'd love a modern take on classic Bungie character styles (which i think we're already seeing in the trailer). The old way elites and grunts looked can't be beat by the 343 versions.
However, I love the environment and landscape art that 343 uses. They put so much detail into forerunner structures; and even though it's different, I do like their take on it.
Halo 2A is a good mixture of what i would like to see in the future. There's so much added detail as an updated take on old ideas, but it still looks so classic.