Yes.

You are stealing they''re intellectual property.

You can''t make Tomb Raider''s Revenge. You can''t make a game featuring a plump yellow stripped cat called Garfield''s Girlfriend.

You can''t make a game that features any copywritten material in any way what so ever. Names can be trademarks, protected from unlicensed use. Characters can be copyright, so no big eared black mice with red pants with buttons on them, sorry.

I still don''t understand why people think that just because they are doing it "For Fun, not Charging" they think it''s okay.

Companies can argue that your free game forever damaged the potential for further income by making a sequel before they had decided to do one. Since they hold the copyright, they can sue you, even if you never made a time, for all the money they will lose because you made a game and gave it out for free.

I know if the realm of art, you can create works of art that include copyright material if your art is making statements about the subject, but I''m not sure those laws have been tested with software, yet.

Copyright laws generally don''t concern profit margins. If someone has a copyright on it, they have all rights to make copies and that includes derivative works. If you feel that you''ve abstracted an idea that you got from another game into a general idea for a new game then the issue of copying becomes a little more difficult to pinpoint. So no, you can''t make a ''Super Mario 8'' game.

Well comrade, anyone is allowed to sue you for anything you do
However, there is a chance that they will oversee it, if they think you''re not worth the effort But you will definitly get a harsh mail if someone working in the company sees your game.
Better create something original, even if it''s harder.

Generally I would say no dont make a sequel, you can problally get away with it if you dont distribute it at all,but otherwise your in a bad boat(at least if you use any of the graphics,music,sound or character names from the previous game/story,etc) unless you can permission of course.