The Finder can do this pretty easily.

1. Open the downloads folder

2. view>as icons

3. view>use groups, view>group by>kind

4. scroll down to the images section, hit the 'show all' at the top right of this section

5. drag the icon size slider at the lower right to make icons huge, scroll around

Alternatively

1. open the downloads folder

2. view>as list/column

3. view>use groups, view>group by>kind

4. scroll down to the images section

5. select an image, hit space to bring up Quick Look, use up/down arrows to move through the images

You can use Quick Look from the icon view too but it's a bit confusing to try and navigate through a 2d grid that's hidden behind the Quick Look.

You could also use either of these methods to isolate all the images quickly, then select them and open them with Preview if you explicitly wanted them in that app, but big icons/Quick Look is usually gonna be a lot faster for uses like "finding that one image in a messy directory".