As far I am concerned, of all his scores, there are only two or three that stick out as works of brilliance, over the rest of his decidedly average output (for a film composer that is-he isn't as sickeningly average as some of the scum masquerading as 'indie' that makes up the pop charts these days-cf. The Kooks, Razorlight, The View).
When he first broke through (with an young Steven Speilberg, whose career mirrors Williams' exactly), he made a massive impact on film scoring with Jaws. A minimalist cello-led number that sent shivers up the spine of the biggest audience cinema had seen until that point. It won the full round of awards (Oscar, BAFTA, Golden Globe, Grammy) and has, rightly, become an iconic piece of music in its own right.
However, since then, he has largely stuck to formula - particularly when teamed up with Spielberg for a overblown popcorn epic comedy-adventure - a catchy motif of about six bars or so, backed up by a full orchestra, with swelling brass and string sections:
- Star Wars (both trilogies)
- Indiana Jones
- Jurassic Park
- E. T. (for which he, perversely, won the full round of awards again)
- Hook
- Superman
- Home Alone
- Harry Potter
It is unfair to single out Williams for this discrepancy - it is commonplace in Hollywood composers by such as Howard Shore, Hans Zimmer and James Horner.
His best composition, arguably, was the violin score for Schindler's List, showing that, like Spielberg, when he wants to make a serious contribution to the art of film, he can be brilliant - but he is content with churning out the formulae.
Compare him to other composers, who haven't got as much mass recognition. My personal favourites are Danny Elfman (The Simpsons theme tune, Edwards Scissorhands, Beetlejuice, Nightmare Before Christmas), Alf Clausen (composed the music and songs for each of the 400+ Simpsons episodes, and was criminal overlooked for Hans Zimmer for the Simpsons Movie), Ennio Morricone , Bernard Herrman (Taxi Driver, Psycho), Lalo Schiffrin (although some of his 80s stuff hasn't stood the test of time well-at least he was trying something new, unlike Williams), Thomas Newman (American Beauty, Six Feet Under theme).
Individual films have brilliant scores also (which, naturally, weren't even nominated for Oscars) include The Shining, Requiem for a Dream - both of which pushed new bounds, utilizing a small number of instruments - and Ry Cooder's solo guitar in Paris, Texas. Sometimes, as Williams might want to acknowledge, less is more...