All antics and other BS aside, Sonnen was a very good pressure grappler. He had fast and educated takedowns, and would even be one of the best in MW today (thats not a huge compliment, as the mw division today is shit and nothing compared to what it once was)
His striking was always basic, only slightly elevated by some of his PED use. Juiced Sonnon could throw a fairly good straight right, but everything else was limited.
As everyone has stated above, he had been submitted a lot. Much it having to do with how aggressive he was in many of those grappling exchanges. Tito by comparison was actually much more defensively responsible in this regard.
Comparing Tito and Sonnen is sort of complex, and probably deserves its own thread. I just wish Chael made it into the UFC earlier. Overall he was big personality, solid fighter. But he certainly belonged, and was UFC caliber in the old sense