Yeah, Singer could have made a good or even great Superman movie. His execution was excellent once filming started, and that's why the movie did make some profit and was imminently watchable. Almost all the films real issues were in the pre-filming foundation, and Singer was lucky to be able for some kind of "traditional" Superman film after all the crud the franchise went through in the 1990s.
But the pre-shooting stuff and the foundation of the film kind of killed it. As someone else just pointed out, this Superman was written largely in character from the old Donner films, but subjected to a pretty bad plot. This exposed one of the weaknesses of the old films: Superman was kind of an idiot and a little bit self centered in Superman II when it came to his personal life and his handling of the relationship with Lois, the Clark Kent persona was always a bland masquerade instead of a real person, and his powers fluctuated depending on what the plot demanded (destroying internal consistency), and Lex Luthor wasn't up to par with modern adaptations (though still quite enjoyable as an adversary).
The actual experience of watching the film is nice, and it's only afterwards that the flaws hit you. The acting is good because Singer is an excellent director; again, the issue was in the conception of the characters pre-production rather than during filming. Routh and Spacey were excellent at portraying Reeves and Hackman's Superman and Lex Luthor, but both those old characters just aren't good enough anymore. The plane rescue was excellent, but incredibly derivative of the helicopter scene in STM, killing some of its awesomeness. And the movies climactic reveals and conflicts had either unfortunate implications or painfully stupid solutions:
Superman has a son from Lois Lane!...Apparently from before he left for the Krypton he already knew was blown up...And apparently she doesn't know he's Clark Kent, thus kind of killing any sincere commitment and forward thinking such a usually moral man has...And unfortunately convincing the audience that yeah, Richard White is better material than Superman, considering he's just as brave and steadfast but much more open and honest...So this film's idea of Superman is kind of a loser.
Superman must stop Lex Luthor's growing continent!...That he wants to sell the land from, after wiping out the world's most powerful economic nation...That has kryptonite imbedded in it to take away Superman's powers!...So he lifts it-wait what? You just said it took away his powers-HE LIFTS IT INTO SPACE!-That doesn't answer the question and is that all you have for the climax-
ALL THE WAY! TO SPAAAACCCEE!-But that's not interesting, and that makes this the third Superman film to lack any kind of physically engaging antagonist-
AND HE DOES IT WITH A PIECE OF KRYPTONITE STILL IMBEDDED IN HIS BODY!!!-Oh now you're just deliberately aiming for an ending more nonsensical than him turning back time!
All that's story problems, not directorial problems. He had a hand in the mistakes, yes, but if you gave him a good enough script, he'd be fine. I think SR and MOS defined why Goyer and Snyder had a better approach than he did, but not that they're better film makers than he is. And while I prefer they're style and take on the mythos, I can understand why some believe he should have been better.