i just started watching more T2 and there are a lot more silences during the games.
Being able to pick up on small details, understanding what a team is doing during the round and being hyped/selling the importance of a game are what makes a good caster in my opinion. Recent example is Achilios casting the FPX games during Shanghai, that was hype as fuck "AND BERLIN WILL GET IT DONE, WHAT IN THE HELL IS THAT?"
I also like it when a caster picks apart a bad play, Steel does that.