It is hard to say how much the edition has truly changed. A definitely apparent change is the random charge ranges. Movement phase is extremely important because of that and the new wound allocation system. The placement of your models is incredibly crucial.
Some have argued that assault is now dead; but it still has the same brutality as in 5th. Assault allows for a greater precision in killing particular models, especially at different initiative steps. Most of the units that wreck ass in close combat still do.
Vehicles die much easier now, which I find to be a boon. I like hull points, and it doesn't add a crazy rule or table to the game. Random terrain, fortifications and other random aspects don't entice me much.
I am still working on my thoughts for my Arkham Tournaments. Will post more.