It's not a terrible movie by any means, it's just average. Which in itself is a disappointment because the expectations were higher given the quality of director and talent attached to this ip.
Spoilers ahead.
Cons -
Ikaris and Sersi just never clicked. They had no chemistry whatsoever. This is pretty big considering how important their relationship is to the plot.
Dane and Sersi were slightly better but still...
I'd lay the blame here on Gemma Chan, her acting left much to be desired.
Same goes but Salma Hayek, but fwiw her role was comparatively minor.
Too many characters introduced in one movie. They tried their best but it is a bit bloated.
Not enough action. You'd think this would help because it'd mean more time to flesh out the characters, but no.
Pros -
Druig and Makkari - The chemistry was off the charts. It's easy to see why they are fan favorites.
The humor is toned down. Not every other line is a quip from the entire cast.
The final action sequence - Ikaris vs Makkari and Phastos vs Ikaris was fantastic.
The philosophical question posed by the plot was fascinating as well and very well handled I thought. Especially, Kingo's stance on it.