This is long, I'm sorry. For the record, I didn't HATE X3, just disappointed especially after seeing SR (yes, I liked that movie more than X3) and considering what Singer could've done with the third (final?) entry in the series. If X2 was his Wrath of Khan, he likely planned (as was rumored during the very early pre-prod news) to shoot X3 and X4 back to back to conclude the series properly, going off of how Spock's arc was handled in the first four Trek flicks. X3 just felt a bit blocky to me, with cheap characterization, muted new characters (Angel & Colossus) which contrasted with Nightcrawler in X2, it barely slid by with a B- for me. There were just as many things wrong for me as there were right, which I can't say for the first two films. Enough of that though, ever since X3's credits rolled I wondered what could have been if Singer had kept the project...
- I still think Singer was foreshadowing in X2 with the Cyclops/Phoenix fight. He knew with that two second shot of Jean's reaction after the mutation machine thing was destroyed in X1 exactly where he wanted the story to go. Cyclops under Stryker's influence attacks Jean, in Singer's X3 we probably would've seen the same scene flipped but more tragic and intense as it wouldn't have ended as well. Jean is now Dark Phoenix and Scott takes it upon himself to stop her, ending with both or just Jean dying. I don't know if Scott would really be capable of this but we don't know how Singer would have realized Jean's Dark Phoenix power on screen. However, I think with the liberties they took with her powers in Ratner's X3 it only made sense for Wolverine to stop her.
- Prof. X may have died, judging by that line Scott had in X1, though it was probably just to show his devotion to the Prof. more than foreshadowing his death.
- Sentinels would definitely have been in this one, as well as the Danger Room, though not just ONE weird looking sentinel in a lame Danger Room session (not counting the setting which was a nice nod to Days of Future Past). Both (as I recall from the X1.5 DVD stuff) had been intended to be on film since the first film but correct me if I'm wrong. No doubt with the budget this flick would've been given, there would have been a really great Danger Room session and possibly a fleet of Sentinels.
- I think there would've been a lot more Wolverine and Scott interaction considering Jean taking center stage as the antagonist. Some above said Singer's X3 would've been Wolvie-centric again, but Ratner did the same thing! There was just so much filler but it really did continue Logan/Jean's story. I think even after the apparent resolution of Logan's story arc in X2, it'd be too much of a risk to remove the focus from the character through whose eyes the audience had been seeing the story unfold since X1.
Overall I think it's safe to say Singer's X3 would've had more action than X2, would have included Beast (again going off of scrapped plans from X1.5 & X2 DVD stuff)as the only new addition aside from picking out screen-worthy mutants from those cute little cameos throughout the first two, a beefed up role for Scott (Singer obviously loves and trusts James Marsden, just look at Superman Returns) but yet another Wolverine centered story. X2 was Singer's Phoenix tease, X3 would've been full-blown fiery ***** from hell. That brilliant little cliffhanger with Phoenix's outline in Alkali Lake was cheapened by what we got in Ratner's X3. It's really unlikely, but I really hope they release some sort of alternate X3 comic series or something with Singer writing. Even an interview would be nice just to know what we (that is, those of us dissatisfied) missed. *sigh* what could have been...