Welcome to the wonderful world of the Legal Minefield, often referred to as Grey Area.
Taking Pacman as a case study, Pacman himself is a trademark so you'd have to change the lead character - that isn't as hard as it sounds considering modern Pacman games have already evolved Pacman's appearance. However there's no problem in you making a maze game where you have to run around collecting pills and avoiding the mazes' law enforcers, an ethical question maybe, but no legal problem.
If gameplay was trademarked then computer games would have died a death in the early 80's as a passing fad and we'd have gone back outside and not turned into a bunch of obese keyboard tappers.
Actual work such as sound, graphics, code is copyrighted - the length of a copyright varies on country. In China copyright expires in the time it takes to write out the import documents, in Great Britain I think it's 50 years - but basically if it wasn't written by Mozart then it's copyright and if it was written by Mozart than the recording of it is copyright [by the orchestra]...
DampeS8N raises an interesting one, level layouts being copyrighted. I wonder how true that is, imagine a 2D driving set in a desert with the odd shrub to avoid - kinda hard to copyright... If we're talking a Quake level then it's easy to see how that would be copyrighted - but if the graphics are different would it be recogniseable... I don't think level design is copyrighted - yet it's probably the one bit that makes a remake closest to the original.
Taking Pacman as a case study, Pacman himself is a trademark so you'd have to change the lead character - that isn't as hard as it sounds considering modern Pacman games have already evolved Pacman's appearance. However there's no problem in you making a maze game where you have to run around collecting pills and avoiding the mazes' law enforcers, an ethical question maybe, but no legal problem.
If gameplay was trademarked then computer games would have died a death in the early 80's as a passing fad and we'd have gone back outside and not turned into a bunch of obese keyboard tappers.
Actual work such as sound, graphics, code is copyrighted - the length of a copyright varies on country. In China copyright expires in the time it takes to write out the import documents, in Great Britain I think it's 50 years - but basically if it wasn't written by Mozart then it's copyright and if it was written by Mozart than the recording of it is copyright [by the orchestra]...
DampeS8N raises an interesting one, level layouts being copyrighted. I wonder how true that is, imagine a 2D driving set in a desert with the odd shrub to avoid - kinda hard to copyright... If we're talking a Quake level then it's easy to see how that would be copyrighted - but if the graphics are different would it be recogniseable... I don't think level design is copyrighted - yet it's probably the one bit that makes a remake closest to the original.