Second episode is rather tight on ammo. Barons of Hell are now regular enemies. And there are also Cacodemons. And you get the plasmagun. So, there’s a bit more variety.
But the level design is somewhat hellish, with mazes for the sake of mazes, and endless amount of crates. Crate mazes:
And there are again some one-time-secrets. Containment Area is especially nightmarish in this sense.
“Halls of the Damned” is funny, because they added a false exit, that is actually a trap.
The cyberdemon was first introduced as the boss for the second episode as well. Which is a lot of investment, to have that huge sprite just for a boss. And as a kid playing from a keyboard, I would have been scared shitless by that. Although now it’s such an easy fight on a large arena with a lot of pillars for cover.