Tough crowd.

Others have nominated the ones that came to mind (like the Stitch Dance Party), which lasted about a month. A stage with no seating and no shade. I would add the Test Track singers they rolled out when TT went down for the refurb back in April (plus not properly listing to closure dates on the park calendar).
As for the mention of Carsland in DHS, you obviously haven't been to DCA. Carsland is fantastic. RSR is in my top five of favorite rides. Hopefully they won't repeat the mistakes with LFT. Not that the ride is bad, it was just poorly executed. Our last night in DCA, LFT was the last ride we took. The wait time listed was like 20 minutes, but it took ~45 minutes because the CM crew insisted on gathering the balls (since removed) and distributing them to each tire. Basically doubling the load time for the ride. Then they managed to screw up the collection of the triangles that are given to the guest like the Dumbo chits for one load. The CM running the ride board also managed to stop the ride for no apparent reason in the middle of one load, and the ride had to reboot to run again. Oh, and on another time we rode it, one of the beach balls struck the CM running the ride, so the ride stopped and again had to reset to run again (which takes 5-10 minutes).
Also, while I don't like the thought of losing LMA (our DD6 loves the show), the backlot attraction is useless in its current state after LMA took over a good portion of the backlot.
Lastly, I'm not sure if Narnia was mentioned, but that attraction was a waste of space and time.
-Kevin