Disturbed - they are not so bad and draiman is a good frontman but they are too much a production rather than actual raw energy, they are very formulaic. they aren't bad live put on a good show.
Korn - They pretty much suck, hate jonathon davis' voice and really boring music, they have a few bearable songs. Absolutely suck live, also they butchered a classic Floyd song so that never goes well in my book.
Linkin Park - once again too much of a production and formulaic, they are there solely to be catchy but they just attempt hook after hook nothing really interesting in their music to me. I guess the new album was different but it sucked for other reasons.
Green Day - I'm just not a fan of the genre they helped create at all, pop punk. Punk was only good back when it had that raw energy in the seventies.
mainstream isn't necessarily terrible for me I like Muse and Mars Volta which I both would consider mainstream bands but most mainstream bands are bad to me these days because I am not a fan of the big genres right now and in recent times such as modern rock, pop punk, indie, nu metal. You go back to the early nineties with the grunge movement and that for me is the last time the mainstream had a lot of good to offer. Bands like Alice in Chains, Smashing Pumpkins, Soundgarden, Pearl Jam, Stone Temple Pilots, Jane's Addiction, and Guns N' Roses were great.