Diaz: Last Hours of Purity is a good weapon mod. Somehow Wildweasel managed to introduce muzzle climb/recoil mechanics into Z Doom.
Unlike many modern-day tactical shooters, though, the BFGs are still slaughter devices, even if they need reloading.
You'll want to use the bipod for the RPK, though. Rat-tat-tat, hellspawn!
Also, don't forget Immoral Conduct.
Also also, play Harmony if you haven't, if only for the curious novelty value of it being a George Lucas Throwback to Doo M clones of all things.
As a total game? In terms of the gameplay? The graphics?
Tough call. I like Doom 1's texture set more, but Doo M 2 has all the cool monsters. Also a better final boss. HEY MISTER SPIDER I HAVE A BFG AND YOUR DAY IS RUINED.
E1M1 will always be the quintessential Doom song, remixed or no.
Serious sam...? Maybe. But i always found most of his weapons where Awesome but Impractical. All of the weapons in doom, even the holyshitthatwasabigexplosion BFG, have their place.
I vaguely remember using a double-bladed chainsaw in one Doom game. I think it was a PS1 port. It tore demonspawn up but good.