Also, if you plan to make money, it might be a good idea to try to bring at least something unique to the genre.
Why else would anyone want to buy your game?

Because you bring it to a platform the original isn't on, or is crap on... such is the case with Worms which is what started this thought process; I'm a massive fan of the game and the iPad version is such a let-down I almost want to make my own just so I can play it!

If only I wasn't so busy that doing stuff for fun was infeasible

I've been playing Worms recently on the iPad and been reminded how great it is. I was wondering if I created a clone called 'Grubs' or 'Maggotz' which was clearly a clone, where do I stand legally? You can't legally protect a game style can you?

The game style of Worms is a genre that long predates that game - http://en.wikipedia..../Artillery_game . I played Worms on my Amiga, and Tanks years earlier on a BBC.

Also see http://en.wikipedia.org/wiki/Warmux , http://en.wikipedia.org/wiki/Hedgewars .

Or were you thinking of something specific that is unique to Worms?

But as always, anyone can sue you for any reason, and given that apparently rounded rectangles and finger movements are worth a billion dollars, even if other people have done it before, if you're in the US, who knows... It's a question of what risk you want to take. Since anyone can sue you for any reason, and it's better not to getted sued at all, then perhaps it's better not to ever release any software at all. But then, most of us here presumably haven't chosen that option.

You can get sued for anything, and regardless of whether you can or should win a court case, the mere threat of having to shoulder the cost of it could shutter or bankrupt you.

In general, you can't protect gameplay, but at least in some recent cases, specific gameplay has been protected. That case involved a Tetris clone, which as far as I recall, did most of the usual things people do when cloning -- new art and music, add some bling, add some minor additions to gameplay, etc. Still, the court came down against them, citing specifics of gameplay--the size of the grid, the mechanic of removing lines combined with the scoring system, the shapes, rate of fall, etc, combined with the fact that the only additions to gameplay weren't significant or integral enough to make the game play differently than the original.

Frankly, in a world with Zynga and their blatant rip-off tactics, I think this is a good thing overall, just so long as we don't end up with individual gameplay mechanics being able to be protected in isolation.

The Tetris/Xio judgment (it was a summary judgment) specifically said that gameplay itself is NOT protected; only the "expression" of the gameplay.
The judgment showed side by side screens of Tetris and Mino, and concluded that there was no significant difference in the two games expression of the basic gameplay idea.

So it looks like if they had (for example) changed the dimensions of the screen, made the tiles people in various contortions (instead of block shapes), and not followed tetris so verbatim etc. they would have been ok.
I provided a link to the actual judgement in a prior post on this. It's only 39 pages; the real meat starts on page 24:

"To separate ideas from expression, the parties offer competing
definitions of game rules, but I do not need to articulate a rigid, specific definition.
While the unenviable task of dissecting a game’s ideas from its expression is difficult, I
am guided by case law and common sense, and find that the ideas underlying Tetris can
be delineated by understanding the game at an abstract level and the concepts that drive
the game."

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