Well, they don't. Not in terms of whether the movie is good from a quality perspective. Box office numbers mean the movie is popular and financially successful. Not that it was well made.
I think it depends heavily on the critic. Different critics review films from different perspectives and have different backgrounds. I mean, when Ebert was alive, I'd trust him to, usually, give a film a fair review. It might not change whether I liked the film, but he was usually concerned with things like the film's narrative structure and the quality of the craftsmanship involved in the filmmaking. By contrast, the folks at Entertainment Weekly or your local newspaper may just say "I liked it" and then describe why they liked it. In that sense, it's just some person with an opinion, no different from any of the other folks who bought a ticket that weekend except for the fact that they have a "megaphone" of sorts to project their opinion. So, yeah, critical reviews don't NECESSARILY mean a film is well made.
Also, Leonard Maltin gave Laserblast 2.5 stars. Also getting 2.5 stars or less: Taxi Driver, Animal House, Blade Runner, The Big Lebowski, The Shawshank Redemption, etc.
How valuable are those critical reviews again?
Again, they don't. Not in terms of the quality of the film. They speak to the popularity of the film. That's all.
Look, a film can be well made but dull as paint. Or it can be poorly made and still entertaining. I don't think it's a stretch to say that Transformers 1 is a BAD film. It's got awful cliches, horrible acting and writing, the fight sequences are nothing special...it's just large robots blowing stuff up and beating on each other for 2+ hours. But it sure was popular and it sure was entertaining to a lot of those people in spite of basically being a B-movie with a big budget.
By contrast, I think, for example, that Blue Velvet is a well made film. It is, however, creepy, weird, and probably NOT enjoyable to a lot of people. It was critically lambasted when it first came out, although critics have warmed to it over time. What does that say about critical opinion, though?
I'm sure plenty of us can come up with less-than-popular but extremely well made movies. There's also a question of what purpose the movie is attempting to accomplish. Is it just trying to be an adventure roller coaster ride? Then we can compare it to other similar films within the genre and determine how it compares to them. There are, usually, examples of extremely well made films within a given genre, even if that genre doesn't exactly get nominated for Oscars on the regular.
Think of it this way. McDonalds' food is popular and sells extremely well. McDonalds is also garbage. I don't think anyone here would claim it is good food, even within the "genre" of fast food joints. I'd argue that there are plenty of other burger joints out there that do a MUCH better burger, even if they aren't as popular or financially successful. Five Guys, Shake Shack, Goodburger, In & Out Burger, etc., etc. You can find better burgers out there. So simply saying "But it makes so much money!" or "But they've served over 1 billion people!" doesn't really speak to the QUALITY of the food. Just its popularity. See what I mean?
Now, personally, I enjoyed Into Darkness. I thought it was well done for what it was, and was a damnsight better than the first film in the Abrams Trek series. But appeals to popularity, financial success, or certain critical reviews which really are little more than "I liked it because it was fun" or "I didn't like it because I didn't like it," don't really get to the quality of the film itself.