It was one of the things which I found to be teh biggest let down. The figth was anticlimactic, too easy, and not interesting enough, unlike the first fight, which was superb. This one felt like a button-smasher, everything they claimed this game couldn't be, unlike the fight in 1, which was intelligent and tactical, especially after the prelude to it in the Silver Warrior Pan fight, which remains my favourite boss batle of the trilogy. I'd have loved to have Satan take multiple forms, with the possession stage being the final part or penultimate, where it leaves Gabe in a real predicament, it's a heart-wrenching gambit. You think that Satan's been defeated, after an epic clashing of light and shadow / void and chaos magic hearkening back to the first confrontation. The possession could come either before or after the epic 7 headed dragon form, in which Gabriel also has to take to the skies in draconic form.
The setting was also a bit lame. I hated the design of the Leviathan, and the look as they're fighting in space just came across as a bit daft. Much more epic would have been to set it before Dracula's throne. show it as a battle for the title of Prince of Darkness, and then maybe for some of the fight, have it be transported to the gates of Hell, and in front of Lucifer's throne, with the lines of reality almost blurred.
I also hate Satan's redesign in general. He looked crap, especially compared to just how perfect he looked in 1. His weird eye colour change also didn't make much sense. Beefcake Satan just..... just lacked a lot, and he lost that sinister thing you'd expect of him, looking fair and beautiful, but with that undercurrent of corruption that snakes it's way in, showing his true nature.
As for Carmilla, while I mostly quite liked her redesign as a facade of her 'humanity', in comparison to her dark, Lord of the Vampires, appearance, which I loved, I found the huge tits a bit of a distraction in a bad way. They were too in your face, even though they do sort of work considering what Carmilla is - a seductress. However, not everyone appreciates an eyefull of tits.
I think Alucard's redesign was one of my favourites in the series. He looked fantastic, especially after they made him look pale and bloodless, as opposed to almost looking like a drow elf.

I love this version of Al as much as I love his SotN-onwards incarnation.