I really can't see the difference between Expert and Infernal BBQ. They look the same. Even the dmg you take seems the same. I think they did a way better job with difficulty balance/changes on Rabi Ribi than this game. Imo it should be a lot faster and more hectic. Tevi feels a lot slower when it comes to the chaos. Rabi Ribi on Bunny Extinction is just bananas hard. Also the + and ++ modifiers just make the enemies way too tanky. Their HP and defense is just nuts. It just makes the fights way longer than they need to be. it's not like they are really that much harder, they just take longer. I really hope they do a rebalance patch on difficulty because it could of been executed a lot better = I.e. more bullet density (like a lot more), faster (turbo feels better and should be standard for higher difficulties, speed should increase with each difficulty along with frequency), along with taking more damage and enemies being tougher and reducing your item count (you get way too many healing items with no restrictions, you should have a lower cap with each difficulty).
Some specific patterns are modified, and there's a couple new ones, but otherwise its just minor scaling. I did find the increased damage noticeable in the early game before you get all your survival options, but once you have an endgame loadout it's not very different. Actually, if you rest at your bed, Infernal BBQ is actually just called Expert++ there.
Well, I have played over 80 hours at this point... so its mostly just due to how much I played since release, than anything. My friend has finished 4 playthroughs by now though lol.