Cosmatos, like already mentioned, appeared as more as a front to the leading stars in some of the films he is credited as director. Stallone always liked to take over, and that is not to discredit Cosmatos's contributions, but Stallone was the one who wanted to call the shots. He did this on many of his films, where he isn't credited as director and his ego got in the way, by wanting to discredit other's intelligence.
Apparently, Kevin Jarre started directing Tombstone until he was replaced by Cosmatos, and if Kurt Russell really directed he did a pretty darn good job, but he hasn't been credited as directing anything.
He made fun movies. Even if he only acted as a "front" on some movies, it doesn't make the movies any less enjoyable. "The Cassandra Crossing", "Of Unknown Origin", "Rambo: First Blood Part II", "Cobra", and "Tombstone" are my favourites.
What do you think this is, a signature? It's a way of life!