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This forum thread post (full thread here) contains a really useful comparison of the various third-party N64 controller-stick replacements that are currently being developed. While the N64’s controller assembly was prone to wearing out after long-term use, in terms of the history of video gaming, it stands out as important for innovating the way the players could interact with the games of the first generation of 3D gaming. The N64 controller was particularly deftly designed (compare the threshold-angles of the various controller-sticks under the heading Sensitivity), and it allowed for the revolutionising of video game concepts by facilitating a precise level of control–think Super Mario 64.
One particular analogue stick replacement that shows a lot of promise uses an assembly not dissimilar from that used in GameCube controllers. This replacement has the long-desired feature of long-term durability, but it isn’t as accurate (in terms of step analogue step-skipping, response-time, and being far too sensitive relative to the controller’s dead-zone–see the data produced from the poster’s fantastic trials) as the official OEM N64 controller-stick.
Despite the fact that none of these replacement analogue sticks are perfect, the amount of money you would spend giving them a trial shouldn’t really exceed the risk of them not meeting a satisfactory standard.