So far, I've played through Chapter 1, 2 and 3 (more on that later). I wouldn't call anything I've played bad per se, but the level design reminds me more of Serious Sam 2 than in does any of the encounters, which isn't necessarily a bad thing, but the levels in SS2 had a lot more stuff going on in the environment and when the size got large enough, included vehicles. Now, obviously, you can't backport vehicles into SS1, but the levels do feel a bit too much in places.
To get into specifics:
Chapter 1 is probably the strongest, but the negatives I mentioned as a whole still apply. The last level being a series of back-to-back arenas isn't a bad idea on paper, but they all look very similar and are too big for their own good. The theme stays consistent, if a bit gaudy with the repeating faces everywhere and some very loud music.
Chapter 2 is a work in progress, but what's included is a mixed bag. Since it's named after a legend, I was expecting something more grandiose, maybe something similar to the South America chapter from TSE, but the first level just all blends together into a yellow-orange mush. The mushroom caves are more interesting, but I don't really see the connection between 'city of gold from a legend' and 'shrooms'. I'm hoping the rest of the chapter will try and tie these things together, when they're done.
Chapter 3 is another strange one. Again, the name evokes some kind of sunken city or mixing of old and new tech, a la Sirians in the two encounters, but it's instead a frozen wasteland crossed with the Kleer planet from SS2 of all places. It keeps crashing on the fourth level, in a section that takes place after the ice taxi. No clue what's causing it.
Overall, this is a pretty interesting project, but it's not something I would recommend over stuff available on the workshop in Classics: Revolution. At least, not yet. It's promising