Lucas had (and to some extend still has) great visual sense.

But he was never too good with actors. Even Ford said that he's 'impatient with the process of acting' and most times his only advice was 'faster and more intense'. You can really see that.

He had a great cast for the original and even there some scenes are a bit 'stiff'. Not to mention the PT...

Also ANH lacks of some kind of emotional depth (e.g. your home planet has been blown away? so what, you can still come up with dozen funny one-liners 5 minutes later) and sometimes feels a little rushed.

He can make great visuals and action but i agree that he isn't a very good director.