I haven't eaten at either (yet!), but a friend of mine who has taken over 40 trips to WDW (!!) emailed me her opinions on nearly every restaurant in WDW, and she had this to say about LeCellier: "generic steakhouse. just kinda eh, from my experience. seriously, go to yachtsmen steakhouse instead"
She insists that Yachtsman is the best steakhouse on property. I can't offer any opinion on that, but I did go ahead and take her advice, and booked an ADR for Yachtman in May. I'm sure either would be enjoyable, though- she's sort of a food snob, so I imagine she's just extremely hard to please.