A test comparison of Standard Blendshape vs Blendshape Combination System (BCS), developed by Daniel Pook-Kolb. (stargrav.com/bcs.php)
You can learn to setup a high-end feature quality facial rig using BCS toolset at Puppeteer Lounge. ( puppeteerlounge.com/rigging-workshop)
Apply here to learn: puppeteerlounge.com/apply
P.S. The Gollum character by Weta Digital was based on such a system for facial articulation. BCS is free for educational purposes.