Factual error: During the plague when the fire and rocks are falling from the sky, they fall behind a statue of Rameses and are seen through its hollow eye holes. It makes for a great image, but that would mean that the statue's eyes were punched out like a mask, even though before they were just carved into the stone.
Continuity mistake: After Moses accidentally kills the guard at the temple, someone points out Moses as the killer and they point straight up. However, we see a shot from behind Moses while he stares at the fallen guard and the angle in that shot between where Moses stands and the fallen guard and the crowd around him is inconsistent with the scene where someone points Moses out. The body and group have moved from just below the scaffolding to several feet away.
Factual error: Ramses' sphinx was established in record time. Given the time between Moses' leaving Egypt and his return, there would not have been enough time for that Sphinx to be constructed. If the movie had conveyed the 40 year span between Moses' leaving and his return, the construction of that Sphinx would have been probable.
Other mistake: When Ramses and Moses are chariot-racing, Moses' facial hair and eyebrows are black instead of dark brown.
Revealing mistake: When the princes are racing with chariots in the beginning, they pass a painting on the wall. Ramses turns his head around to look at it. Look at his hair tail, it blows straight towards us - against the wind.