Flooring Tile - ceramic tile on slab foundation

I am in the process of removing the linolium flooring in my laundry room and bathroom. Between the linolium and the plywood on the slab is what looks to be a layer of thin set of something used to float the floor smooth. Should I just scrape off the thin set and refloat the floor, or is it better to replace the plywood as well (Its a little beat up from my scaping and some water leaks in the past ten years). Or, is the best way to tile directly onto the concrete slab? ANy help will be greatly appreciated.