I don't, actually.
Second big flaw is that it's unaccessible. That is a flaw, but it's what you expect in a mod - if this was a game that'd be an issue, but a single creator hardly has resources to create a 32 level campaign that super well tutorializes every mechanic of the game. It's a bit of a charm of game mods.
I mean, I recall identical situation was with Demon Souls/Dark Souls before it blew up - everyone was complaining that it was too hard and impossible and ergo it sucked.
But then Bloodborne came out, which actually managed to tutorialize Souls gameplay well, and suddenly everyone is a Dark Souls fan.
I believe that eventually, one of the HD fans is going to create an entry-level Wad for Hideous that teaches you most key mechanics, and it's gonna become MUCH more popular, and a better mod in itself.
Yeah, there are other problems - creator seems to have a bit of fetish for realism/difficulty and seems more interested in creating difficult game than in creating a fun one, but it does add to the peculiar kind of charm this mod has. It's not a mod for everyone, but it doesn't make it a BAD one. Tactical shooter fans like it because it's not like tactical shooter genre is particularly common - I mean, there's original Rainbow Six games, Ghost Recon, ARMA, Stalker and its predecessor from the same creators Codename Outbreak, Full Spectrum Warrior [sorta], SWAT 3 and 4, indie roguelike Receiver, first Delta Force and... uh... That's it?
Hideous Destructor means that you get almost infinite supply of maps (Doom maps) that you can play as a tactical shooter. Actually, if you find what OBLIGE settings work well with Hideous, then you get factually infinite supply.
It's not gonna be as polished as a proper tactical shooter like Arma or Rainbow Six, but it IS an appealing concept.
That wasn't me, and I don't actually believe that. Again, I just believe that people who dismiss the mod outright without giving a fair try are scrubs.