I'm sure my TiFaux recorded Unchained Reaction so I'll need to watch it. The thing with it was is that I got bored with it as there just wasn't enough too it to make it interesting. Watching the teams assemble the machines just wasn't interesting and the show seemed to delve a lot into the "reality show drama/bickering" that's common to shows like this.
I also think the show needed more involvement from Jamie and Adam, though I know that wasn't in the cards since J/A lived and worked in San Francisco and were still doing Mythbusters while UR was done in Los Angeles.
Really the show made me realize how much I missed Junkyard Wars.