Series 1 is the best series, followed by 2. I can't believe the people saying 3 and 4 are better, it got rubbish then, I stopped watching in the middle of the forth! Conrad was an awful dweeb, not a patch on Jason. Then the new ones, and that girl from Liverpool, all just SO boring and annoying. It was sometimes like watching a bunch of whining kids - a worse version of Hollyoaks.
It was miles better when the proper (original) characters were in it, strong characters with good, solid story lines. Tanya, Jason, Sal, Donna, Frank etc. crisp and confident with exciting, fresh individual characters that all riled different emotions. The later series were average to poor, like the writers were just churning it out with no feelings, not like the first ones which were taught and powerfully done, truly excellent (and I went into it VERY sceptical to be shocked at how much I loved it). Series 1 is Fantastic on its own, but series 2 is very worthwhile too as it ties things off well.
Don't bother with the later series, just get these two amazing roller coaster rides in a bargain boxset - it goes downhill from here.