What I'm gleaning from week 1 of the round so far is physicality, which comes in many different forms:
1/ Athletic ability (ie speed)
2/ Endurance
3/ Strength, ability to win the second ball
I think the most elite teams have a mixture of both physicality and techncial/tactical prowress. However the newly promoted clubs and lower half teams are going to be looking to press the perceived higher rated/more well resourvced clubs in a way to create second-ball situations where they can win out physically. Hull did it, Sunderland did it very effectively last season, Ipswich & Brentford all showed it as well in their games.
I think teams that have fairly thin squads and are light on the physical side of the game are going to struggle this season.