Then buy the lot, you will not regret it. Some are better than others, naturally, but even his worst is like Tom Holt on top form.

I'd read them in order, personally. Though that might just be because that's been my experience of them.

As others have said, the style changes after The Light Fantastic, but the first two books do a lot of scene setting and character building that feed into the later works.

edit - Troll Bridge was published in the anthology 'After the King: Stories In Honor of J.R.R. Tolkien' - http://tolkiengateway.net/wiki/After_the_King - buy that too. Is all good.