I've used clipless pedals for 8 years, Shimano SPD for the first 6 and then Time ATACs. The direct power feel is always nice, but I always had trouble with foot and knee pain, even with really floaty Time pedals. Then this year I sold my frameset to buy a new one (Surly Ogre), spending a couple of months riding a borrowed bike. That bike came with some old BMX/DH flat pedals, identical to the DMR V8. I was skeptical at first, but then I got used to those pedals. To my surprise no foot or knee pain, with any shoes I had on.
With my new bike ready I went ahead and purchased some last gen slim pedals, the Superstar Nano Thru Pin.
Man, this things are great. Really big confy platform and so thin and grippy that you can actually apply a nearly circular pedal stroke.
I'm not sure I'm ready yet to leave the power transfer feel of clipless, but these last generation of flat pedals are really really good, everyone should try them