Bad may be a bit harsh, but I don't think I can say it's good by any stretch of the imagination. I think mediocre is about as generous as I could be with it. I appreciate what Singer tried to do with it, but the whole film was unnecessary and came across as more of a rehash than anything for me.
I'll admit I haven't seen it in a while, but I doubt a rewatch would change my opinion much.
I like to pin Cyclops getting fucked on in X3 as Singer's fault as well. If Marsden didn't sign onto Returns, I feel his character wouldn't have got shat on as much in X3. It's not to say that Cyclops would've finally gotten proper treatment, but anything's better than his pathetic showing in X3.