Slitherlink is not additive

(tags game, puzzle, Dual Screen)

My DS Lite has Slitherlink loaded. (I finished Sudoku Deluxe but I'll post that later). I find this game really frustrating in comparison to Sudoku. My best time for an easy puzzle is something like 01 minute 55 seconds. My worst time is 70 minutes. An easy puzzle is a 10 by 10 square.

I think the problem is that solving (guessing?) a part of the table doesn't add to solving the whole. You could be locally correct but it might not mesh with that part over there. Either than or I suspect I am used to the quicker validation in games like Sudoku.

Its thrilling to get a sub 4\ minute time, but then I tried a normal puzzle and the size of the board just scares me (18 x 10).