This artwork was commissioned by me and drawn by the very talented Márton Kapoli: Reddit, Instagram
I have permission to distribute this work.

A little tribute for Guncaster, in my (very based) opinion one of the best and my personal favorite Doom mod of all time, created by the one and only Pillowblaster (of Russian Overkill fame).
Guncaster is a little on the OP and broken side, but it's way more balanced and cohesive than RO, and it plays fantastic on higher difficulties.
If it wasn't a Doom mod, I would honestly consider Guncaster one of the best games I've ever played. It's so fun and varied and has way more content than some AAA titles I've spent $60 on, all while being FREE.
There's plenty of run-gun-fun-ness in Guncaster to last you a good while, so I would recommend a hefty megawad like either the original games or anything with 30-ish levels, like Eviternity, Maps of Chaos, Sunlust, Valve, Hellbound, or just long levels like MMDCXIV.
Guncaster has a really satisfying glide/flight mechanic, so you might consider maps with some verticality.
My favorite combination that just nailed everything perfectly was Guncaster, Dark Encounters for the maps, and a separate add-on for Project Brutality's enemies (a special GC-compatible version exists). The scifi/fantasy themes of Dark Encounters fit in perfectly with Guncaster's aesthetic, and the levels' verticality felt so good with the flight mechanic. There were a few secrets you could break by just gliding up to them, but it wasn't a big deal. And PB's enemies so you have plenty of enemy variety to go along with all the mod's guns, spells, powerups, upgrades, bells, and whistles.

The first skin is the Cygnis Suit, designed after Cygnis Flaynithere, the half-dragon protagonist of Guncaster. The Doomblade is based on the Brimstone sword and the shoulder launcher partly on the Longhorn revolver.

The second skin is the B.A.D.A.S.S. (Battle Armored Dragon Assault Strike System) Powersuit, a super-fun power armor that grants regenerating health, air strikes, rocket punches, even secondary BFG cannons with regenerating ammo! The shoulder launcher is based on the Augur Railgun. Oh, and the BADASS doesn't expire and can be used whenever you want.

The last skin is the Deadmaker Armor, based on the mod's Deadmaker Mask, another stupidly OP and fun item that turns you into a colossal demonic dragon that can punch out cyberdemons, breath a scorching torrent of hellfire, and level the entire map with mighty fiery slams of your beefy arms. Which also doesn't expire or have a use limit.

...Oh, did I mention you can combine both the BADASS and Deadmaker Mask now to become the unholy cyber-draconic Mechamaker?