Yeah I heard horror stories about the DLC so it seems like it needed a patch.I really recommend it.
Except for the TAG 1 final boss (unerfed), I had a blast with all of it.
This honestly makes me want to try more of those Serious Sam games(as I only own the 3rd game) and test Serious mode. Mental mode sounds insane with invisible enemies.Serious Sam's always been an interesting example of good hard and bad hard in the same game.
The standard final difficulty (out of five) is Serious, which drives enemy counts and damage way up to the point where common enemies can three-shot you from full health without armor and a direct hit from a big enemy with armor will still leave you at death's door. But it doesn't adjust enemy health or player damage at all, and nicks DOOM's idea of giving you double ammo, so the whole thing winds up being this incredibly tense skill check where you're forever teetering on the knife's edge but all your knowledge of how the game works still applies and your resources can keep up with the increased carnage.
Beating that unlocks Mental mode, which is balanced like hard difficulty rather than serious, but with the caveat that the enemies are invisible most of the time and only briefly phase into view every couple seconds. Complete insanity. The score multiplier for it is higher than serious mode though, so if you're chasing high scores, uh, good luck.