I remember playing the NS1 mod for HL1 shortly after it came out. You could feel the raw "spirit" the developers put into the game. It was not only challenging multiplayer competition, it was also an atmospheric and downright creepy/chilling. The pre-existing HL1 textures, sound effects and sounds with the custom ones really gave NS1 a nice kick in the atmospherics area. An area NS2 severely lacks in.
Levels in NS1 were bigger of course, and made you feel more immersed in the levels, like you were actually inside of a base. Granted, a lot of the rooms lacked details like chairs & such but that was a consequence more of gaming back then.
NS1 felt more industrial & sci-fi. I'll never forget the dark, spooky rooms, fog, waterlogged rooms and corridors as I battled strange aliens.
NS2 levels feel designed directly for tournament play and literally nothing else- they in essence feel like Unreal Tournament 99 levels such as "Face" http://liandri.beyondunreal.com/CTF-Face
For me the small details from NS1 such as interactive doors with buttons, lifts, huge blast doors and other custom effects made the game much more replayable and enjoyable. In NS2, these features are missing and it feels quite barebones.
This is why I didn't support them making their own engine. It took so long to build the engine that NS2 has suffered for that time loss. Even their newly announced game Subnautica will not be using the Spark Engine because of its limitations.
I bet they thought all these developers would be rushing in to purchase licenses for the Spark Engine but so far none have and for good reason.
What are your thoughts?