About 4. Style over substance:

Coding style (apart from formatting) can be crucial for understandability, so it's important to have a critical look at it when reviewing. For instance, consider the following snippets:

  void myMethod(FooBar arg) {
    if (arg != null) {
      arg.foo(something);
      for (int i = 0; i < arg.bars().size(); i++) {
        arg.bars().get(i).baz();
      }
    }
  }

vs

  void myMethod(FooBar arg) {
    if (arg == null)
      return;

    arg.foo(something);
    arg.bars().forEach(baz);
  }

Even though they're functionally identical, they look wildly different. These things can hardly be judged by an automatic process like linting, so it's important to manually do that.