In a sense, this is a good. Rather than cram a sequence of action-packed scenes into 90 minutes, you have twice as much time to slowly digest each one of them. On the other hand, if you're used to 90 minute bang-ups, this one might appear to take forever. Hanna must stop this criminal gang just as they are about to pull off their last big job. However, one shouldn't see Heat for the story, or even for the action.
Heat is mostly about character development.
We rarely see a gangster's personal life scrutinised in detail in Hollywood movies and Heat is a welcome change in that direction. However, Heat turns out to be somewhat of a self-parody. It's hard to empathise with the robbers who kill people on whim. It's also hard to empathise with the cops who don't seem to really care about people but are simply interested in winning a gun fight at all costs.