It's difficult to decide on my favourite season of Lost; watching them concurrently, with the exception of the third, each seemed to get better and better. The introduction of the hatch, the flash forwards and the time travelling was superb and kept the show feeling fresh and progressive. For me, the peak was seasons four and five, which was often nothing short of astonishing television
Sadly, it transpired that the writers had bitten off more than they could chew. Where the sixth season should have provided insight and resolution, it actually introduced unnecessary new characters and inconsequential plotlines, so that the moments every Lost fan had been waiting for were either rushed in a completely unsatisfying manner, or just didn't happen at all. Key characters were just disposed of (Widmore, who had been built up as crucial to the show was simply shot) and the Jacob's 'powers' were explained by some daft 'magic potion' nonsense. It was a slap in the face to everyone who'd faithfully given it their time. The final 'twist' made very little sense within the context of the show until that point, and rendered much of what we'd enjoyed watching inconsequential.
Terrible final season aside, this is well worth anyone's time, for the show at its peak is incredible. One day I'll go back and watch it all again, but for now what feels like a betrayal by the writers still stings.