I've always really liked this film.
I think calling it simplistic is a fair criticism, but simplistic doesn't necessarily mean inferior. In fact, being simple is one of the overarching themes of this movie. It is 40 years of American history as seen through the eyes of a very simple man.
The way it catalogues American history - by having one very dumb man experience it all - has always been the strength of the film to me, because it's done very well. The movie streamlines archival footage (often melded with a digitally inserted Forrest Gump mind you), period music and various historical milestones from ping pong diplomacy to the appearance of AIDS, to recast the history of post-World War II America for us in an interesting light. I also think the way they portray Forrest as the accidental founder of numerous cultural trends is a nice touch.
The claims that the film is marred by a heavy conservative bias are rubbish. Certainly, Forrest often does things without questioning them and the sexually promiscuous Jennie dies of AIDS (which, if you will recall, actually happened to A LOT of sexually promiscuous people in the 80s). But I think it is fairly obvious that Forrest Gump is not a satirical attack on the post-war liberal movement of the 1970s and it doesn't just single out hippies; it pokes fun at Nixon, war junkies, the South, blacks, whites, liberals, corporate America (Forrest, the quintessential idiot, becomes a corporate mogul). The fact is, it's a tongue in cheek look at everything American. And in any event, the character of Forrest is not fundamentally conservative, though his views on religion may imply otherwise; what he is, is a fundamentally a good person. He wants only to do right by his friends and family, whether black, white, gay, straight, promiscuous, insane, or otherwise.
Of course, being a Zemeckis film, the landmark usage of CGI is noteworthy in and of itself.
As for the criticisms that the movie is cliched or stupid, I don't think they carry much weight. "Sorry I ruined your Black Panther party" is not a stupid line of dialogue. Given that Forrest, a Medal of Honor recipient and upstanding American solider, just gave a speech at an anti-war rally surrounded by burnt-out veterans and then sort of wanders into a Black Panther headquarters and breaks up the meeting... the conscious juxtapositions here lend themselves to lots of intelligent analysis, in addition to presenting a humorous scenario.