Perfectly mediocre, insomuch as the virtues; an excellent cast & an interesting subject / historical period in this case, are balanced by corresponding flaws; the performances are either too much or too little & all the complicating contours of the man & his times are sanded down into generic 'Oscar bait' gimcrack.
Probably a decent enough intro to Trumbo & the Red Scare for the completely uninitiated, at least.