The pilot reported that the airplane had just undergone an annual inspection, and this was the first flight since the work had been completed. After a normal preflight and run-up, the pilot departed, raised the landing gear, and during the initial climb, he felt an "intermittent shudder" from the engine. He reported that all of the engine parameters appeared normal, and when he reduced power in the climb the shudder stopped. The pilot subsequently decided to land immediately; he reported that on downwind in the airport traffic pattern, abeam the runway numbers, he recalled that he lowered the flaps and landing gear. He further reported that the approach was stable, and that the airplane touched down on the left main landing gear first, and as the airplane settled to the runway, the "right wing tip dropped to the runway." The airplane subsequently skidded off the runway and into terrain where the left main landing gear collapsed. The left wing and fuselage sustained substantial damage. The pilot reported that throughout the traffic pattern, he was "intently watching the engine monitor" and could not recall observing the three green landing gear down annunciator lights prior to landing, however, he recalled that the gear unsafe warning light directly in front of him was not red at any point during the flight. He reported that after the accident, when the airplane was lifted up for recovery, the right main landing gear was found retracted in its well. A witness that was located on airport property reported that he observed the airplane on short final, and the right main landing gear appeared to be retracted, but the left and nose landing gear appeared to be down. He subsequently observed the airplane touch down on the left main landing gear and roll for "quite some time" before the right wing contacted the runway. Examination of the landing gear system by a Federal Aviation Administration (FAA) Inspector following the accident found that the nose and right main landing gear functioned normally through multiple cycles. The respective green landing gear annunciator lights functioned normally, and the nose and right main landing gear fell and locked into place through the activation of the emergency gear release handle as well. The left main landing gear was disconnected from the system prior to the tests due to damage sustained in the runway excursion. The investigation was unable to duplicate any operational discrepancies with the landing gear system.