Everyone is after a different experience for a festival, not everyone will agree on the quality of the lineup, I think what Sziget have tried to do this year is book relevant artists, depending on the genre you like will maybe decide on if you think the lineup is strong or weak, the sziget lineup this year seems to be more leaning to the dance/house/EDM side, but that genre of music is by a mile the strongest most popular genre there is currently.
All of the other lineups above seem to be more nostalgic than relevant, maybe I am wrong but I cannot remember the last time I heard that Placebo/Lenny Kravitz/Offspring/Massive attack/Pj Harvey had a hit song ? not saying they are not great performers but they are not relevant to todays market.
Sziget, may not have the biggest names, but 90% of the artists are relevant in todays market and will appeal to most of the people.