I have some criticisms/suggestions. Please understand that I love that this exist at all, but I have practical considerations which might make it better.
First, I don't like that the sides are plates. Since it needs to site on top of a block, the fact that it is a face-up plate makes it float. I know it can be supported from the sides, but it's a naturally-floating block. It should be full-sized, vertically.
Second, and that has a lot to do with the first, the size of the sides on the 5x5 is such that if you place anything bigger than a half block on the sides, it shows up through the doors of the elevator going up or down. And because it's a plate, you get some weird spaces when filling the sides with half blocks. If you don't do that, then you need a shaft that is even wider, despite the plate already giving a "buffer" around the elevator itself.
Third, there's no fully enclosed option -- both the 3x3 and the 5x5 leave a fall trap on the floors the elevator is not at. It would be nice if there was an elevator with a closed door where the elevator *isn't*, and a "filler" 1-high block to be stacked on non-floors to make up the shaft.
Finally, it would be really nice if there was a way to connect a trigger to a floor to make it automatically call the elevator. I blame three08 for giving me this idea with his remote switch and powered door mods. Oh, wait...
I'll wrap up with my top five list of favorite mods on alpha 17: powered doors, remote switch, elevator, cctv (because I haven't actually used it, so it's in fourth, for now), and... I haven't found a mod worth of being number 5, so I'll leave that open. And, no, that's not my list of favorite
three08 mods.
EDIT: I'm feeling a bit stupid now that I see the SDX version does half what I suggested, but the first two points are still relevant!