I'm just going for a laugh. The fact that GWAR and Apocalyptica are playing is just bonus, and I don't remember/care who else is on. Last year I knew about 5 of the bands, had heard of about 6 more, and I still had a mega rad time. The only real dissapointment for me was Opeth.
If Testament played it would be badass! They're one of my big favorites at the moment, as they have been for a while. Seeing them supporting Priest on Saturday was mega, but seeeing them in their own show in Oxford last Thursday was the fucking bollocks! I could watch that band every night of the week and it would always be awesome! At least until permanent tinitus set in.
As for bands I think should play this year, Godsized. They're a fucking ace band, at least on record. One of my lecturers recorded a 5 track EP for them last year, which I was supposed to help out with, but the scedule changed and I couldn't make it. The result was badass, and I'm fucking gutted I missed it. If they're half as good live, they'd slay at Bloodstock. I also reckon it'd be cool if Down played, and Clutch. I'm very much enjoying the heavy groove style metal at the moment.