Sure, you could play Doom 3 in its boring, by-the-numbers first-person mode, but why would you want to when there's a mod to transform it into an isometric 3D shooter stuffed full of chunky excitement?
The mod Z-Hunter comes close to accomplishing this feat. While you can't play the original game with an isometric view, Z-Hunter does offer "8 maps, 2 unique weapons, unique player animations [and]over 20 enemies custom designed for this style of play", according to the description on the website. Slap in a custom soundtrack and you've got quite a package. There's even a short back story to help get you in the mood. It mentions pussies and maggots, but it's not what you think.
No co-op or deathmatch functionality from what I can see, but that doesn't stop it from being infinitely awesome.