Alzheimer's is a bitch, so I'm both very sad he's dead and relieved he's no longer suffering.
I got to see him when he visited NAS Alameda scouting locations for the Star Trek 'Save the Whales' movie. The real USS Enterprise was homeported there at the time and I guess Paramount was figuring on shooting some scenes aboard her. For whatever reason, it fell through and another, fossil-fueled carrier got the job instead (USS America IIRC).
Anyway, we all wanted him to come aboard and tour the enginerooms, shake hands, get photographed, etc. but the command nixed it. He did charm the pants off the base though. A Marine air group was stationed in Alameda and, as a pilot himself, he mixed perfectly with them all.
He and the fellow who played the helmsman were the only actors I felt were 'real' in ST:TOS. They rest all seemed to be charectitures; crotchety doctor, alpha-male captain, somewhat alien alien, etc. With just a little suspension of disbelief I could believe that 'Scotty' and 'Sulu' actually did the jobs they pretended to do on TV.
I know squat about acting, so that's my rule of thumb for it. If I believe you as the charecter you're playing, you've acted well. If I keep remembering you as another character while you're playing this one, you've done poorly.
To Absent Friends,
Bill