I didn't like it because it featured a series of defeats for the good guys and the ending left you hanging.
The reviewer for Commentary also panned the film. He wondered why Darth Vader was alive in the second episode when he had apparently been blown up and presumably killed in the first. He apparently missed Darth Vader's escape. That scene is so brief that you'll miss it if you choose that moment to blink your eye.
That's why many (including me) did not like it at the time, but when viewed in context with the other two, it's great.