To be fair, one of the most telling examples of how engine sharing can lead to similar visuals is on PS2 - Jak and Daxter and Rachet and Clank. Despite Jak and Daxter trying for more cartoonish stylings while Ratchet and Clank tries for a more futuristic sci-fi design, both games clearly look like they were spawned from the same tech. Both share that Lego World look, where objects stand out as complex polygonal constructs because surface personality afforded by texturing is so sparse. Things look shaded all over in color rather than covered in intricate patterning.
Another example is Konami's Cy Girls and MGS2. Reportedly using the MGS2 engine, Cy Girls resembles a P.N.03 set almost directly in a MGS2 smoothly metallic indoor locale.
Games sharing the same technology are not doomed to a look-alike fate, of course. Creativity by the graphic design team is the true determinant for how distinctive a game's visuals can be.
On one end of the spectrum, the creators might choose to mold the design around a console's capabilities... famous examples of this being when Miyamoto gave Mario a mustache (and a hat) to sidestep the difficulties of expressing finer facial detail with NES sprites, and when Naughty Dog designed Crash as an orange bandicoot because of how well the color stood out in PSX's muddy 3D. When taking guidance from the hardware capabilties like this, some designers may indeed end up pushing a console in similar ways, and their games may bear areas of resemblance as a result (Team Kojima games like ZOE, MGS2, and the celish-shaded ZOE2 all seem to exist in a universe with stylishly smooth objects/characters and bountiful effects... although, owing to the team's creativity, each game certainly has many areas of individual visual style also.)
But on the other end of the spectrum, creative graphic design, that's perhaps less compromising to hardware temptations, shows just how varied and distinctive games can be made to look. An imaginative dev like UGA on Dreamcast, with Space Channel 5 pt 2 and Rez, and Smilebit on Xbox, with Jet Set Radio Future and GUNVALKYRIE and Panzer Dragoon Orta, probably worked with a similar technology base across their multiple titles while still realizing wholly separate and unique graphic designs.
