...but gave up because the game is SO bad. Maybe I'll give it another go in the future on a lower difficulty. It was a horrible experience.

Rose-tinted glasses indeed.

Perhaps a coop would be a better option?

You have to kinda cheat to enjoy co-op, such as setting the respawn rate really low so you can stock up on weapons. And since nothing carries over, you have to start with the default loadout on every level. And some things don't work well in co-op + the robots use a different AI online. It's not ideal for a longplay format.

Unless this is you saying you want to do D3 co-op

Basically.

It's a shame nobody has written an overhaul to the coop mod.. You know, 24 years after the game was released :/

There's only so much you can do with it . Actually an enhanced co-op mod was released in like 2010 or something like that. It basically added some features like being able to move players around (incase they were stuck), higher PPS, a few other tweaks.