I some ways I can agree that some aspects of Star Wars are a little bit fantastical. But that's what made it great in my opinion. It wasn't just straight Sci-Fi - it was Science Fiction crossed with Fantasy.
You also have to remember when the film was made, and the technology they had back then. As for storm-troopers, I don't think they look silly. Having a helmet that is (supposed) to protect you from knocks and blows and shots and poisonous gases is a great idea. Thing is, storm-trooper armor acts like it's made from paper-mache, as it doesn't even stop rocks from knocking the trooper out.
When you compare it to some of the more "modern" sci-fi films, yeah, some aspects were a bit silly. But back then it wasn't, and I still think that Star Wars had more heart than say, Avatar.
About the only things I can think of that I found "silly" with the original three films were:
1) All the higher-ups in the empire having British Accents (yes I get the symbolism, it's still stupid)
2) The fact that jedis limited themselves to light-sabers. I get that they can block shots with them, but seriously you could use more than one type of weapon guys.
3) The Ewoks. God damn, those stupid furry little ewoks.
4) Some of the droids acting too human
Yoda wasn't silly in the original star wars - he was just a wise sage who could do amazing things. He only became silly when they decided to make him a hyper-active CGI frog in the prequels.
Speaking of what was silly in the prequels:
EVERYTHING. You had those idiotic combat droids which were far too slapstick, you had Jar-Jar, you had Hayden Christensen behaving like an angst-ridden emo and a jerk to boot, you had a collection of CGI aliens who tried to be funny, but whose routines and "jokes" looked like they were taken out of a three stooges episode, you had the Boba-Fett army which was perhaps one of the most blatant fan-services in all of history... the prequels were a mess.
But I don't think there's much wrong with the original film. It might be corny to Generation Z-ers growing up with iPods and "The Matrix", but I was born in the 80's and still had to watch things on Video-tape. Even in the early 90's, Star Wars still packed a punch. I still think it will age well.