Although I'm not a mason, my grandfather was and I've (very unofficially) seen his regalia. They're the epitome of a non-secret secret society, many lodges have websites with their lodge meeting dates for the next few years posted up, and indeed their lodges are proclaimed pretty obviously - the Southampton Lodge is next to the West Quay Shopping Centre and the words "Masonic Lodge" are carved over the doorway. They're fundamentally a bunch of (usually older) men who do a bit of a funny dance in private, have meals and do a lot of philanthropic work. There are plenty of books around, some of which are fairly dry but list the reality of lodge meetings and what goes on behind closed doors, and some of which are full of rather entertaining conspiracy theories. The Masonic Library in the London Grand Lodge is open to the public, which goes to show just how secret they really are.
It's an interesting organisation, they give millions to charity. In 2008 they gave half a million to the Scout Association, as well as substantial sums to Outward Bound, Barnardo's and various Air Ambulance Trusts.
Essentially they are a community who look out for each other. My grandfather for instance would go out of his way to get his photos developed by a Mason Chemist rather than the chemist on the high street. Similarly when he had a life-threatening blood infection, then had he died, there would have been a place at private schools for my mum and uncle funded by a masonic benevolent group, as well as some support for my grandmother. In some ways it's quite similar to the armed forces benevolent societies that help look after war widows and families. Indeed the MoD itself contributes to boarding school fees for children of servicemen (more often long-term commission than the short 4-5 year commission, and especially for kids who are at GCSE/A-level age and need a bit of stability, although the MoD also tries not to move people to new postings 6 months before offspring have major exams and suchlike if the parents choose not to go down the boarding route).
However, that loyalty only extends so far. It's pretty unthinkable that a lodge would cover up a crime committed by a member - in actual fact they'd be more likely to cast out a member who threatened to put a stain on their reputation and may well be the ones to report them to the Police.
It's really not that creepy an organisation unless you believe the hype.
As for the main objection, which seems to be one of corruption amongst politicians or those in public office, the Masons are a positively minor issue compared to the old boys networks that run through institutions such as the London Gentleman's Clubs, the Mason's just get attention and bad rap because they're "secret". Right up until you google them... you can find out more about the Masons on google than you can about Private Member's Clubs in London, the sort of places ministers hang out and rub shoulders in private.