characters of the show

I loved this show in it's early days (not nearly as much of a fan of the more recent episodes) but there was one fault that I always noticed (unless it was in my head, which it may ell have been)- there are very few consistent charatcer traits- Jonny, other than being the partner of Janet and having an obsession with biscuits seemed to change on several occasions, one minute he was the nice guy and the sensible relatively sane character next he was incredibly dim witted and in some ways insensitive aswell as being juvenile occasionally (admittley this jvenile nature was probably the most sustained of his charatcer attributes)and often for no reasons seemingly connected with the epsiodes plot . I also saw similar things happen with Donna, who I found a very diifcult charatcer to analyse, as her character did not seem to stay in any way the same, though in my own eyes she was often rather two dimensional. Infact, essentially Gaz was the easiest chracter to become familiarised with as his typically masculine, sex addicted ways often lasted. Does anyone else agree? or is this just my interpretation?