Nope. There's a part where it endlessly spawns kleers and there is absolutely no way to win. I don't know if it's been fixed or not, since that was back when it first came out.
That was fixed in the first patch. :V I myself never encountered it when I played it and that was just after the first patch.
And come on, isn't Serious Sam supposed to be silly and not serious at all? I mean, not quite SS2 silly, but there's guys with chainsaws and pumpkins on their heads for christ's sake.
Yeah I agree. Croteam kinda got some shit because of that, and they say that SS3 will be at least as silly as SS1 was. And as I said, they included the required entities and models for recreating the intro, but they couldn't got the level into the game with a patch because it would have screwed up the Steam leaderboards and stuff.
Though I wonder if it's possible to add it as a SS2-style video, as the SS3 engine is based on the SS2 one. Hmmmm. I might check this out in the editor.
By the way, the Highlander Reptiloids appearing everywhere was caused by the Co-Op mode, as it adds extra monsters and encounters. :V
Edit 1: *watching Part 6* Some places, SSHD is harder because there's actual physics now, and frankly, SS1 wasn't built for that, they didn't really changed anything about the monsters, save the beheaded soldiers having extra weapons.
Edit 2: Dunes is my favorite level in TFE too. :3