You need the wads (where's all the data). If you have doom on steam, you can compile something like GZDoom, and copy the wads from steam over

Doomsday is great (apart from the occasional segfault at the end of a level). It works well with Steam files and it has its own launcher so you can customize things easily.

Of course, but even Romero has released free WADs so content is not an issue for true Doom fanatics.