I would liken the Sheraton brand to Hilton's Doubletrees. While there are some nice ones out there, there are quite a few real dogs as well. One of Marriott's strengths (or some might say weakness) is they adhere pretty strictly to some set standards and don't let hotels vary much from those. The result is you know what your getting at most every FS Marriott (as it was the same as what you got at the last Marriott you stayed at.)

Note that other Marriott brands might allow for more variability in layout, design, etc.