Bioshock 2, and BI for that matter, really cleaned up and streamlined, in a good way, the combat from B1. They had this two hand system where left click activated your main weapon and right click your power.
The reason Bioshock 2 was so much better than BI in this regard, is the options that you had at your disposable. There were about 10 weapons you could carry at one time, each with different secondary uses and ammo types.
Tackling each encounter with the plethora of weapons and powers you had at your disposal actually kept the game very fresh.
Why? the DLC has been subpar so far. In fact, the whole game is subpar.
I would recommend holding off indefinitely. Or rolling through on easy to experience the story. Increasing the difficulty only makes the enemies bullet sponges, and ends up highlighting some of the gross shortcomings with the gameplay.