To paraphrase The Sound of Music, how do you review a problem like Machete? What are you going to do? Criticise it for being stupid and over the top?
Some background. When Tartan Quarantino and Robert Rodriguez did their Grindhouse project, their objective was to make pastiches of 70s exploitation flicks. As part of this, they and some other filmmakers made some spoof trailers of other kinds of 70s exploitation flicks, including one by Robert Rodriguez called "Machete". You can see this trailer here: http://www.youtube.com/watch?v=R10ljA0-sHs - go ahead and watch it, I'll wait.
Now, it would appear that a sufficiently large number of people drunkenly hung on Robert Rodriguez shoulder at parties, saying "dude, you should, like, totally make that as a full length film", until he either started to think it was a good idea himself, or else thought that it was probably the best way to stop people doing that.
In any case, that's what this is, this is an utterly over the top, nonsensical film that contains pretty much every scene in that trailer. Yes, including the ones at 1.40, and 2.25. And that's the plot, such that it is. Some guys hire Machete (Danny Trejo), an ex-Federale, to assassinate a senator, but he's really there to be the fall guy so that the senator's policies on tight border controls will gain some traction. Also somewhere in the plot is Steven Seagal as a Mexican Drug Lord who's basically there to be the big bad guy to have a machete vs sword fight in the final act.
Also drifting around the plot are Jessica Alba as a good-guy immigration cop and Michelle Rodriguez as the head of a good-guy illegal immigration network.
Not that it makes a lot of difference. It's mostly an excuse for Danny Trejo to slay as many people as possible with as many bladed objects as possible. Violence is basically Itchy and Scratchy style stuff with loads of blood and dismemberment (you'll see four men decapitated with one machete blow in the pre-credit sequence.) The dialogue's funny, mostly in the hands of the bad guys, handled with idiotic aplomb by Jeff Fahey, Robert DeNiro, Don Johnson and Steven Seagal.
I suppose, ultimately, this is a joke that doesn't quite warrant an hour and 45 minutes, and certainly doesn't manage to be coherent for that long. But a lot of it is bloody amusing, and amusingly bloody.