I often read Berdych categorized as a "big hitter" and considered as similar to Del Potro and Söderling.
I personally do believe that it's more complicated than that : I would put him between Federer and Del Potro/Söderling.
Berdych has more variety and also uses more the opponent's pace to counter like Federer.
He's less powerful than Del Potro and Söderling, uses hardly any spin while the other two use more spin (less Söderling on the backhand), and he uses more changes of pace with accelerations like Federer.
He has more mobility.
I remember that I found the match against Söderling in SF of RG 2010 as an interesting example in that matter.
Last week against Del Potro, they showed that Del Potro had played 75% of his shots cross-court ... while Berdych had only played 50% of them : his mind is more about variation.
Of course he's not like Federer either : I would say he's a special kind of player between those two kinds of players.
Maybe some people who know technique better than me can describe it better