Yes, there are plenty of very good unis which aren't part of the Russell Group - from the Guardian rankings, the following top 20 unis aren't in it (though I know some of these are joining shortly): St Andrews, Durham, Lancaster, Bath, Exeter, Loughborough, Surrey, Buckingham, York, Leicester and Heriot-Watt (?!). Queen's Belfast, for example, which is in the RG, is down at no. 53, and Sheffield at 42, Liverpool at 45 - and so on. So really I can't understand why RG is used as a measure of rating universities.