It aged, face it.
I used to love this movie as a child and I still enjoy it now.
But recently i rewatched the OT and... well... I have to say that I was disappointed.
I couldn't see the charateristic menace and the stage presence of Darth Vader, i only saw a ridiculous guy in a ridiculous suit, the costumes aged badly, the acting, except Mark Hamill and (of course) Cushing and Guinness is pretty bad, the plot is inconsistent, and it all seemed like a campy, cheesy b-movie.
Anyway it's certainly far from bad and it's still better than Return of the Jedi, which had a lot of potential but failed thanks to those little CENSOREDCENSOREDCENSORED that CENSORED and CENSORED CENSORED Ewoks, but even ROTJ is far from bad.
But hey, the first chapter doesn't always have to be the defining, and The Empire Strikes Back is still a Masterpiece.