Ooh good luck. I do think there is a 'civil service culture' of sorts although of course it is a enormous and diverse organisation so no one person's experience/department will be the same as another's. It does suit some people, some people absolutely hate it 
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Purely from personal experience I would say it is really brilliant to work somewhere where the drive and purpose of the organisation is to benefit the nation and the public rather than to make profit, and for the most part you can tell this is what motivates people and it makes for a nice atmosphere.
Civil service organisations particularly the bigger ministerial departments do tend towards a somewhat conservative (with a small c), meritocratic type of culture, perhaps even to the point of being a old-fashioned, so for instance familiar people, systems and ways of working are clung to for dear life; experience, long service and knowledge are often hugely valued, sometimes at the cost of new ideas/innovation; people are generally well respected by their colleagues but this can be based more heavily on seniority/grade than on actual ability; staff have a lot of 'rights' (pension scheme, sickness benefits, job security etc still virtually second to none and there is often quite a lot of opportunity for flexible working, flexi time etc) but sometimes this is too rigidly stuck to and hinders change and true flexibility - pros and cons all round!
People often complain about the risk-averse, highly political type culture of the CS but IMO this is just as bad in the private sector, it just manifests differently. For instance just to take a very stereotypical example (and of course this isn't universal) in the private sector poor performance (of staff members or contracts or projects or whatever) will usually be fairly ruthlessly and brutally axed, no mercy or chance to improve given, (because the organisation won't risk second chances), whereas in the public sector obvious problems can be left to run for a long time (don't want to risk upsetting the apple cart), sometimes this is great because given time and support things can change for the better but obviously also sometimes they just fester and we waste a frustrating amount of time and money for want of someone taking decisive action...
Overall if you have the motivation to serve the public and are of the right kind of mindset where you can cope with the shifting sands of public policy direction/ministerial whim, and are able to navigate and not be driven mad by layers of bureaucracy and slow moving progress, it could really suit you. You probably won't know until you experience it, but I'd say give it a good go with an open mind .