The lack of guitar solos was just one of many factors that put me off St Anger. Some of those tracks had a rather a simple song structure, that they were just crying out for for inclusion of a solo here and there.
I'm a big fan of Megadeth, and one of the key reasons is because Dave Mustaine and Chris Broderick (and Broderick's predecessors) litter songs with plenty of solos. With my belief that Mustaine is not the greatest singer and Megadeth does not carry quite the same aggressive bite of the '80's, I feel that the musical craftmanship and especially lead guitar work help to make Megadeth albums a selling point for my tastes.
Meanwhile, I can think of classic albums, such as Mortification's Scrolls of the Megiloth, or some Napalm Death, which are largely devoid of guitar solos, but riffing gets the job done and they are still a pleasure to listen to. Yet, I rely on other bands, such as Obituary including guitar solos to complete the overall package. If I imagine a band like Obituary not having guitar solos, Obituary may come up a tad short for my liking.
All my favourite thrash bands typically have guitar solos in them, and whether they're just a random set of notes, or structured in nature, really doesn't matter to me - as long as they fit the music.