The Galaxy Note 4 is getting a bit long in the tooth in mobile terms, but that dont think that means it not worth buying especially at less than £400/$500 without a contract. That is a lot of phone for the money and in some ways plenty of people will prefer it to the newer Galaxy Note 5, a phone thats not actually available in the UK.
The newer Note gives you a better camera and faster processor, but doesnt have the removable battery or microUSB slot of the Galaxy Note 4. Both these features have been key to the Note 4s success so were not quite sure why Samsung chose to omit them in its latest phone. We wish it hadnt