You get all the free SD channels dish carries (public interest, shopping, preview, Dish 101, etc) plus any HD channel in the tier (and the SD version of that channel is thrown in too). Plus all the PPV is available for purchase.
It is a good deal if all the channels you want are in HD, you will save some bucks. Even with the price increase it will be $15 cheaper to go "Turbo" vs "Classic + HD".