Some good info here: https://pinside.com/pinball/forum/topic/avengers-definitive-tweak-guide.
Main issues on my game were the black widow ramp needing adjustment with a washer to get it level and raising the hulk arms to prevent ball hang-ups. Both pretty easy to tweak. You may also want to relocate the Loki ball lock plastic. Others had issues with the drop targets resetting but I never had that problem on my game.