I'm quite fond of the LM Koh Samui and have stayed there a handful of times over the last couple of years. It's not perfect and the beach isn't great, but in Samui you get what you pay for. You'll see my reviews on the hotel's thread.
I get the impression that most guests are on package tours, so Platinums tend to get treated very well. You'll meet some of the senior operational management and unless you're there in peak season you're pretty much guaranteed an upgrade to a Pool Access Suite from the cheapest room category. The villas look beautiful, but are a whole different price level. Pool Access Suites are rooms which give you access to a quiet paddling pool type area which can be handy as the (otherwise nicer) main pool can at times be full of loud children. There are various other plat benefits including a happy hour during the lantern ceremony which I enjoy even when by myself.