I'm generally not interesting in weapons mod. What I want is good level design. If the levels come with their own weapons and monsters, then why not, but, while they do offer more diversity, it happens very often that there is something wrong with those, like an overpowered weapon that doesn't feel satisfying or powerful at all, or monsters that have WAYYY too much health (and a zillion of that monster type in the map).
I have played some mods with good, well balanced, new monsters and weapons though, but I've played so many wads that I don't even remember the names (and I generally have a very poor memory for names)
Lately I've played Threshold of Pain which is a good examples of what I've said above : there is a new weapon that's very powerful and which have a high fire rate, but which feels like SHIT to play with. It's a hitscan weapon and where you hit something it literaly sounds and looks like crap.
There is also this new minigun (see pic) with a higher firing rate which is evened out by having to wait a little before being able to shoot again or switch weapon after firing, which I guess is supposed to be some cooldown effect, but there is no sound or animation to represent that cooldown...
Some of the new monsters are pretty cool (although generally they are only normal monsters with different palettes except with faster mobility and firing rate, but well, it works) but some of them like the new "big-monsters-from-Doom-2-that-shoots-fireballs-from-their-two-armcannons"
and the new Cacodaemons have WAYY too much health.
The levels are okay. The mappers used some creepy ambient music and every level has some kind of original color palette (like the whole level is colored like that, can't really describe it, just see pic) and he seems to believes that alone will make the levels interesting. While it does work for a while in terms of atmosphere, the basic and squarish level architecture and layout, the way levels drag on (which again is not helped by some of the new enemies with more hp) and the flaws of the 2 new weapons, ultimately come back to your face and overall it's a pretty average wad.
I don't exactly recommend it, there are much better stuff to play out there which succeed in every aspect.