What more needs to be said? You've got an amazing and faithful port of DOOM 64, a whole new episode, and no more Bethesda login crap required. Doesn't get any better than this!
DOOM 64 is, quite simply, the best DOOM game made on the original DOOM engine and I don't say that lightly. I love the original DOOM, DOOM II, and even Final DOOM but DOOM 64 is a perfect example of a game that doesn't waste any space, featuring tight, creative, distinguished levels that are perfectly designed to be challenging without resorting to needless hoards or dirty tricks (Although the final level is pretty hoard heavy but I suppose it gets a pass, being the final level).
The gameplay is functionally the same as the original DOOM games but the engine has been updated to allow for features such as colored sectors, slight room-over-room (Mostly used for bridges and what not), traps such as arrows or wall-fired rockets, and scripted events which allow for things like radical changes in map geometry, teleporting items, trip wires, and more. The theming leans further into atmospheric horror and gothic design than the original games but the gameplay remains as fast and aggressive as ever.
There's one new gun, unidentified in the game but known in fan-canon (and as of DOOM Eternal, game-canon) as the Unmaker and there's an all new boss monster to fight at the end. Other familiar monsters return for this installment but have had their designs changed, some slightly, some dramatically, and most if not all of them are more powerful than their OG-DOOM counterparts. Lost souls for example are half as durable but attack twice as frequently, making them lethal in large numbers, and pain elementals now launch 2 lost souls at once.
One big thing I love is that secret levels aren't just their own reward - there's a tangible benefit to visiting them that I won't reveal here, other than to say it's definitely worth looking twice over every nook and cranny for those previous secret exits.
What else can I say, it's the best DOOM game of the original era, it's a steal at $5, and if it's on sale, it's a no-brainer. Buy it.
As of writing this is probably the best and most accurate port of Doom 64 around and thankfully with the GOG release, not only is it DRM-free, but it also fixes some very annoying visual bugs compared to the Steam version (probably subject to change, but still).
I play on tv in the living room with a dualshock 4 and this game just worked right off without having to run DS4windows which I need to run in background for most other games like doom 2016, metro exodus... you name it....
This is arguably what the real DOOM³ should've been. Gameplay, level-design, atmosphere, secrets... All top-notch.
In particular, the soundtrack (available on Bandcamp) by Aubrey Hodges deserves the highest praise as it just nails the game's ethereal horror atmosphere.
Do not hesitate, DOOM 64 is stellar. It is, in my book, the definitive 90s old-school DOOM experience.