The Canon Fisheye EF 15mm f/2.8 was a very good quality fisheye lens for when it was released. It is still good today for use on digital cameras, although chromatic aberration will sometimes be obvious on the jpeg created. However, if you also shoot raw, then it is a very easy matter to fix this chromatic aberration (and while you are at it the peripheral illumination) on the raw image and to convert to jpeg using the free Canon Digital Photo Professional software. Then the image will be free from any visible chromatic aberration and the picture will be a lot sharper corner to corner.
It is an autofocus lens but usually you would use it in manual focus mode and set a hyper-focal distance with a low f-stop number such as 11 or 16.
For me, this lens is excellent for capturing the mood of a place because it gives such a broad angle of view. The fisheye look does not bother me and I prefer it to the stretching you get at the edges for very wide rectilinear lenses.