Difficult to score, you want it to be better than it is due to the first movie
TL;DR: It wasn't a terrible movie but it wasn't anything I'd say warrants more than a 5 or 6/10, and I tried to watch it whilst trying to completely forget the first movie but due to it being a direct sequel and Scott throwing in every call-back under the sun, it was really tough to ignore how good the first movie was and compare the two.
Long version:
Casting a fresh face as the lead actor is, imo, always a bad choice when making a sequel. I understand giving people chances but really considering how good the first one was, you really want to at least knock it out of the park with a well-known actor.
Also making a direct sequel is never a good idea, but having a spin-off movie is always the way to go so at least you get the marketing down but you're not having the audience directly comparing it to the first movie.
The plot moved a bit too fast, feels like Scott had to edit out a lot of a scenes due to the runtime. This similarly affected Napoleon, but Napoleon wasn't a direct sequel to a really good movie, so it was easier to rate it higher.
I thought the casting was okay (apart from the lead, he wasn't bad but they needed an established actor), I liked the two emperors, but they didn't get enough screen time to really flesh out their characters, and they weren't really 'evil' enough. I don't think that was the actors' fault, just more a poor script (hence maybe the runtime and Scott probably having to remove a lot of scenes of them, building up their character).
Denzel did a good job, I thought, I think just that the script around him wasn't strong enough, so he also felt the affects with his character and it felt rushed. Same with the General and (spoiler) Lucius' mother, members of the council etc. - all fine acting but that can only take a movie so far.
Similar to Alien: Romulus, there were maybe a few too many 'call-backs' to the first movie. It's fine to have them here and there, subtly, but when it's really obvious it's a bit eye-roll worthy.
I understand why they use CGI for animals nowadays, but they maybe need to wait longer to make them look ultra-realistic. I have a hard time suspending my disbelief with CGI.
The boat battle in the coliseum was.. interesting. I guess it was something new, I suppose, but maybe detracted from the seriousness somewhat.
The party fight scene was pretty good, one of the better parts of the movie, imo. Obviously a big budget so everything looked visually pleasing to the eye from an aesthetic point of view (apart from the CGI - wasn't bad but again I find it difficult to suspend my disbelief).
I'm going to give it a 6/10. I gave Gladiator (2000) a 10/10 just because it is one of my favourite movies of all time. This one had the budget, but just felt quite rushed, felt flat, and relying too much on the first movie doesn't instil much confidence as a viewer.