I think III got a bum rap because it was sandwiched between an all time classic movie and one of the biggest box office draws in the franchise so it always seemed to be looked upon unfavorably and is where the bullshit 'odd movie curse' sprang from. I look back on it now in a much better light - like other posters have remarked it brought so many firsts for the franchise, and aside from the odd slow part or cheap looking set remains an entertaining movie and I rank it above TVH these days, and definitely above the likes of Generations, Insurrection and The Final Frontier.
The theft of the Enterprise remains the movie's best scene and one of my favorite sequences in all of Trek, not only that it captured just the right blend of drama and humor which TFF failed to do (bar the campfire scenes), TVH went way over the top with and TMP which didn't even try.
The special effects were pretty good too - standouts werethe Enterprise on approach to the first spacedock reveal, the theft and destruction of the ship itself were all well done for 1984.
The only things I didn't really care for were the story itself, which was bordering on the preposterous, and the slow ending with all the Vulcan mumbo-jumbo comes across as very cheesy these days, but at least it tried to capture the spirit of TOS.
I'm a big fan of Star Trek III