In the sense that, it is an appalling hereditary despotism and human-rights abuser, a weapons proliferator, a proliferator of religious intolerance, supporter of terrorism, haven for criminality and abuser of the spirit of the Vienna Convention. They supply about 2% of our imported oil, and they buy a fair whack of military equipment from us.
Human rights
Human rights speaks for itself. All meaningful power is vested in the 6,000 male descendents of King Ibn Saud, who collectively choose the Crown Prince and constitute almost the entirety of the executive branch,, whose personal wealth is indistinguishable from and intermingled with state-revenue. They have restrictions for women that would be seen as extreme in Iran, they chop off body parts for punishment etc etc.
Proliferation
In terms of proliferation, Saudi Arabia stumped up billions of US dollars to cover most of the costs of both the Pakistani and Iraqi nuclear programmes so they could see the development of an "Islamic bomb". This predictably led to illicit proliferation in Syria, Iran and North Korea. They also have an agreement with Pakistan to supply them with five or six nuclear weapons on short notice if there is a sharp deterioration of the security situation in the gulf.
They have also contributed considerably to conventional proliferation in the region by importing Chinese medium-range ballistic missiles, and on-selling American munitions and technology. They also contributed by handing over $25 billion to Iraq in the 1980s to buy weapons to fight Iran (before having to cough up $60 billion to defend against the same weapons in the Gulf War).
Diplomacy and criminality
Their abuse of the Vienna Convention is legendary. Every one of the 6,000 or so Saudi princes travels internationally on a diplomatic passport, and they don't hesitate to use it as a shield to prosecution or detention. The diplomatic passport and Saudi Arabia's refusal to sign up to meaningful extradition treaties makes it a haven for criminality, right through from Prince Nayef whose private plane was seized with 2 tonnes of cocaine on board in Paris, to ex-dictators like Ben Ali of Tunisia, to Saudi citizens who kidnap their children and disappear into the kingdom knowing the Saudi police will do nothing.
Financing of International Terrorism
Perhaps most objectionable, they turn a blind eye to terrorist financing, not least because militant Islamic fundamentalism has committed and entrenched adherents and sympathisers at the highest levels of Saudi society (not just in the conservative clerical caste, but also in the royal family / government).
The Taliban are, in large part, are funded by rivers of cash from well-heeled, conservative Saudi donors. Ditto 90% of the Salafist madrassas in the Muslim world, which have had a negative effect on local minority Muslim sects and interpretations, and on Islamic religious plurality. The consequences of this can be seen most clearly for the girl children of Afghanistan and the tribal areas of Pakistan.
Equally, they were one of only two countries in the world to recognise the Taliban regime in Afghanistan from 1996-2001, providing it with diplomatic cover (the other being Pakistan, with whom they're joined at the hip in a special relationship, particularly on foreign policy and nuclear), as well as providing substantial financial support to it and the government of Sudan (which, as it happens, was the other country which acted as a terrorist sanctuary for Bin Laden during the 1990s)
Most egregious is the still-unexplained involvement of elements of the Saudi intelligence service and royal family in the 9/11 plot, by putting their funds and agent networks in Southern California at the disposal of the San Diego hijacker cell, providing them with accommodation, cash, logistical support, etc.
Foreign policy
A foreign-policy made subservient to Arabian oil is a very outdated; Britain now imports less than 5% of its total oil consumption from the Middle East (down from about 3/4s in the 1950s). The Persian Gulf is not as crucial as it once was to international geopolitics.
They buy our weapons, but that is offset by the fact that the cost of those programmes are simply tacked onto the price of oil, and more considering the gigantic bribes / commissions demanded by Saudi princes when they do business with overseas contractors and suppliers.
In the past it may have made sense to view Middle East policy through the prism of energy security. But the equation has changed beyond recognition due to the large decline in our Mid-East oil imports, the end of the Saddam regime and the changed circumstances in Egypt and Iran.
So...
Other than oil, we have essentially nothing in common with Saudi Arabia. When you add up all the costs of Saudi complicity in international Islamic terrorism and financial and diplomatic support for the former Taliban regime and government of Sudan (essentially, we wouldn't even be in Afghanistan if it weren't for Saudi Arabia), the cost to international peace and stability of their funding of Madrassas, their proliferation activities, general tendency to criminality by princes, diplomats) and human rights considerations, I don't think it's outweighed by what they spend on British kit.