The question is vague. What does it mean for the brushes looking like crap? Are they just very rectangular and uninteresting (because you didn't spend a lot of time putting in the details)? Do they lack good texturing?
Inherently, there is no difference in making a brush for Hammer 4 compared to the previous versions. The process is identical. There are some new tricks you can do to make them better looking, like including a env_cubemap. There are also a few more tools for making basic geometry (the torus and sphere tools, for example).
Have you mapped for HL1 before? If you're experienced with that, you shouldn't have any trouble making the transition.