Tried the first level, and have to say, this really is the closest to a Third Encounter as if it was made back in 2002 (which I could already see from your old Third Encounter project)! I like that you were conservative with the new enemies just yet, introducing them slowly and not getting carried away with them like SS2. The level really feels like classic SS levels, and of course, can't help but notice how the first level was made out of the first 3 Theba levels from Sam2000 (or the LotB levels). The very start of level 2 I also recognize from Sam2000. Which is -also- very Croteam-like, since we know that multiple levels in TSE were made out of cut TFE/Sam2000 levels as well. And I love the cut enemies finished and fully realized too.
Man. This just feels so genuine and refreshing, good luck with finishing this, I'm looking forward to it!