Serious Sam The Third Encounter: Approaching The Final - 12 Bermuda Triangle - Dem Li Aru (Serious) 

The second level is surely better than the first, no bullshit-physics parts and balanced difficulty with the very cool idea of reusing the multiplayer maps in a single-player version, a really good level overall with a very simple but effective final boss
Serious Sam The Third Encounter is the project of Steam user ,,R'' M1strz M!strzów M, including three campaigns in three different environments (similar to TSE) which show how a possible Third Encounter would have been in the classic Serious Engine graphics with many enemies and weapons scrapped from the SS Alpha and enemies used in the Bright Island campaign. I've already played the first two campaigns on my channel, and this third part is Approaching the Final
Steam's workshop page:
steamcommunity...
I've played this map in blind run at Serious difficulty. When you see the fades, it generally means that I've died there, or that I went back somewhere to pick up some stuff or that I've reloaded 'cause I let myself be hit too much in stupid ways