Firstly, it was made in 1979, so the effects are not going to be as stellar as they were in the 80's and 90's. And even then, some of those effects still hold up quite well to movies produced today. The modeling work, especially of the orbiting Hercules and Peter the Great nuclear missile platforms, is extremely impressive. The meteor itself is a big, ugly, and rather scary chunk of scarred rock, reminiscent of the Texas-sized shard in "Armageddon". Yes, some of the effects DO look cheesy (the avalanche being the most frequently cited example), but others are quite striking. At worst, "Meteor"'s effects are extremely uneven, but certainly not completely junkable.
Secondly, unlike "Deep Impact" and "Armageddon", the film focuses on the multitude of hurdles that have to be overcome in order to combat the threat. Personal, politicial, and scientific obstacles are given due screentime, which serves to advance the story rather than bogging it down.
Thirdly, "Meteor" is a far more globalized film, as it pulls together Russian, English, and even Chinese characters into the story. The attempt to track the rock and derive a viable solution to knock it out of its Earth-based trajectory is not solely an American one, but instead a closely coordinated international effort. Indeed, even the U.N. is (briefly) featured.
Fourthly, the film doesn't get mired in the 'human element' (as what happened in "Deep Impact" and "Pearl Harbor"). "Meteor" is non-tangential in that it STICKS TO THE STORY, which is the main interest of the viewer (at least, for me). Yes, there is the attraction between Connery and Wood's characters, but it's generally unobtrusive and the screentime limited.
Fifth, Laurence Rosenthal's score is great! Its boldness reminds me of Poledouris' legendary score for "Conan: The Barbarian". It effectively captures both the 'feel' of space and the direness and immediacy of the situations portrayed.
Finally, I emjoyed the acting. Connery, Keith, Malden, and Fonda turn in sincere performances (especially Malden). "Meteor" is an ensemble production in the tradition of Irwin Allen's best disaster productions.
Don't let the naysayers in here turn you off from this underrated gem. If "Deep Impact" and "Armageddon" left you wanting, give "Meteor" a try. Sure, it may not be as polished as those two productions, but it has more going for it than you might think.