I just recently got this and only had In Rock to compare this to. Overall, Machine Head has more solos, puts less emphasis on intensity (vocals and keyboards are not as dominant or heavy) but instead adds in the variety department... the album is a bit calmer, but just as intelligent. It is generally more upbeat, but does not let up in terms of musical perfection. The double solo (keyboard and guitar) on Highway Star is very catchy and passionate at the same time. Maybe Im a Leo has a very laid back, bluesy feel and a real cool riff. All tracks really are fantastic. Lazy has that classic, bluesy riff, with solos coming out of everywhere and Space Truckin' is more simplistic but has a real heavy riff for the time, and sounds very energetic. Smoke on the Water is just a masterpiece period. Basically, what makes this album great is the variety displayed in each and every song, as well as the songs' unpedictability, and how well all the instruments are orchestrated. DP also displays a lot of passion in their play, they poured a lot of emotion into each song. The production is cleaner and more vaired than on In Rock. The only thing one can feel is missing from the album is just the chaoticness of In Rock but hey, Deep Purple is obviously a band that wants to progress. I'm looking forward to hearing Fireball next.