Well me and my brother(rahvin666) are currently trying out Spider line5 (or Stack 5x5) on a five in a line board now here at BK! We are only playing up to the letter J, which makes it a 10x10 board for starters. My first impressions so far of this is that its a bit to slow in starting, not much excitement, BUT as more moves are layed down, the thinking then starts!...see how it goes for now.
Kevin, how about the 'free space' move goes to black only and they can use it at any point during the game.
e.g. If white starts D1 then moves over to A4 on second move, then black could go for the prime sqaure, which would be D4! Hence it would be 'free in space'...or black could use it later in the game if you can see a white winning set up!...or you could vary this by white having 2 free space moves with black having 3! white then would not be such as an advantage(I dont think it is anyway in normal 4x4, but weve already had that debate, SLAYER? lol)