They're a news organization with an Arab nationalist slant (note that nationalist does not mean Muslim fundamentalist). The irony of that fact is that their leanings exist almost entirely outside the US political spectrum, and they tend to be relatively even-handed and diverse in their description of non-arab politics and news (they do lean left in their commentary, though). Furthermore, even though their reporting on the middle east has it's faults, they have far, far better access and investigative drive than any other news agency.
There are two different divisions. There is 'Al-Jazeera', which is for the Middle East - apparently the first news source not controlled by the country's government and effectively a government propaganda outlet for whatever country. The leader of Qatar gives them editorial freedom it seems and they have become very popular because of that.
They seem 'fair', they cover both sides - which pisses some people off. When I've checked them they're often covering some US official giving a speech - they seem to bend over backwards to give a lot of airtime to the US government's statements, more than I see on US networks; but they also give airtime to others, they aired Osama's messages as news, and they tend to have graphic coverage of violent events (which is accurate and news coverage but unpleasant. Darn war being unpleasant).
Then there is the newer 'Al Jazeera America' (formerly Al Jazeera English) which seems to have a lot of BBC staff and influence and stories more aimed for the US audience. I've seen reports on it which put US news channels to shame at telling good, accurate stories about the US.
The poster above says they 'lean left' - to some, the truth is 'left'. So no surprise. In fact, that seems to be the case with a lot of media - if it's 'accurate', it's 'left'.
If John Boehner were to sacrifice an intern in front of Congress with a dagger, a news agency saying he did - much less using the word murderer - would be 'left'. A news channel explaining how the Democrats made him do it and covering it with a tone of 'Democrats CLAIM the speaker did this - while ignoring their own killing like Ted Kennedy at Chappaquiddick, the hypocrites, much less their coverup of their killing four Americans at Bengazi' -that would be fair and balanced.
The only way to see Al Jazeera I know of is on the web, and it's not in English, so not easy to get much from except pictures. The same has been the case for Al Jazeera English, with cable companies refusing to carry it, but now that Al Jazeera bought Current TV, a few more people might get to see more of it. It's about time, with our 'freedom of speech'.
I don't really know of any 'left' channels in the US, I assume there are some in some other countries. There are some 'cover the news in ways that agree with Democrats generally' shows, some of which are more 'partisan' than others, but nothing even close to a counterpart for Glenn Beck and Fox. If someone knows of one, just link me a clip of their referring to Fox 'infiltrating the US' and having to prove not their accuracy but that they aren't traitors to the US when they add a city.
I'd suggest if you haven't seen Al Jazeera America, check it on the web and post your opinion.