It really depends who you ask and what you like in your music. I have loved Moonspell since their first album and I love their live show. They are gothic-tinged metal.
Devil Driver is a whole nother story. I think a lot of people on this forum are so into Opeth-worshipping that there is no way any opening bands will make them happy. This band is yes, a bit nu-metal, but with death and black metal mixed in a bit. They all listen to a variety of bands like Immortal, Emperor, Suffocation, In Flames, Arch Enemy, Motorhead.... so it shows in their music a bit as well. I'm not saavy on the nu metal part of it, but I like the other parts, so it's not THAT bad. They were really popular at all the California shows.
Class of Zero opened at the Phoenix, San Diego, Anaheim and Hollywood shows. They are not on the rest of the tour.