The chief difficulty with OHG is that it doesn't really exist. That is, apart from a few chance survivals elsewhere, nearly all we have is the product of Charlemagne's scriptoria. Most of what survived consists of translations of Latin originals and is, thus, not very reflective of the natural state of the language. Charlemagne had a vast collection of pre-Christian materials but his son had it all burned.
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons