What would have made LoI better is if they added more areas, had more platforming like the ones for N64, and the whip swinging like LoS. They could have also given Walter a second form, but three battles back to back could be pushing it.
Also, Leon is the epitome of what someone in his circumstance should be. He lost someone, but he didn't let his grief consume him. He grieved, but moved on. Mathias did the exact opposite.