I keep seeing people say this, but I don't see it. If anything, it feels much faster. Lol
No kidding. I started playing the original Doom oldschool style, but got bored after one and a half episodes. Tried it with Brutal Doom and it felt much faster and more responsive. The hit reactions were great too. Blazed through all of Doom 1 and Doom 2, and now I'm working through Plutonia and Evilution.
The thing that gets me the most about the older games is how painfully slow most of the weapons are. Even the chaingun feels slow, firing at the rate of a standard assault rifle for most other games. Brutal Doom is somewhat unbalanced, but I thought it was a whole lot more fun.
People might cite reloading as a reason the game is slower, but that's to counteract higher fire rates and generally more powerful weapons. Plus the reloads are all very quick and, in the case of the standard shotgun, can be interrupted.
If it's the finishers folks are citing, those are optional. You only do them if you've got a beserker pack and use your fists in the "rip and tear" mode (as opposed to the "smash" mode). All other finishers occur within normal gameplay (like shooting a wounded demon, or kicking it in the face until dead).
In any case, the Doom I saw here was considerably slower than both Doom and Brutal Doom, with much worse hit reactions from enemies.