Yeah his acting wasn't great. Partially the fault of the director, who is on record of hating working with actors.
Episodes 4-6 worked because Lucas wasn't yet a god, and people would stand up to him. Like Harrison Ford - "You can write this stuff, but you can't say it."
Episode 1-3 might have worked, had Lucas farmed off the directing work to someone competent. Better direction, better dialog, and minor plot tweaks probably would have saved the films.