One of the main things I want to be much improved on next time is for the supervillains and bosses to be much more towering and fearsome. The cross-species in ASM were too small and looked not threatening and cinematic enough.
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I don't believe the best way to make a boss more intimidating is to just increase their size. The Arkham games make this mistake a lot, and they force themselves to keep raising the bar on height until it gets ridiculous.
Titans are big, but bane is tougher so... bigger! Croc is a later boss fight, more difficult so... even bigger! And now we have titan joker for the final boss, he should be more difficult than Croc so... ridiculously more bigger!
Then in the next game they make freeze 7-8 feet tall, you fight Solomon Grundy (a dead guy) with a fist the size of your body and Clayface goes from the height of joker to the height of a giraffe. Bigger doesn't make them look better to me, it makes them look stupid, and even weaker by comparison.
In ASM the heights of the various cross species were pretty much fine. I actually thought Vermin was too big if anything, he's just a rat man after all. Rather than pumping up the size of bosses, I'd rather increase their abilities/skills to make them more equal to the protagonist.
In Arkham city, I was hoping the Rhas al Ghul fight would finally be an instance where you fight a boss who is roughly equal to you in size and ability. Someone that can counter your attacks for a change and move just as quick as you.
Unfortunately you spend most of the boss fight facing hallucinations.