basically all the peeks to the “backside” (ratman’s dens?) from the test-chambers are pretty different, but they were fairly cosmetic anyway.
after the last chamber & the fire/furnace, it’s like entirely different game. Different puzzles, different … everything. Some ideas of original games’ rooms there are similar (like the giant room with many turrents), but execution is VERY different. Which, incidentally, is the place where I left off as the darn turrents killed me repeatedly. x)
And tbh, it’s been few years since I last played portal (any of them). I think I’ve played through portal 1 probably 4-5 times? So I’m not THAT much “in the know” with all the rooms/tidbits.
PGA Tour 2k[somethingoranother] got the same treatment, afaik. Once the servers went down the “campaign” AFAIK became unavailable. I believe some quickplay with stock characters is still available but even in that case the game would be a shell of it’s former self.
Shame really, me and my buddy liked the private versus matches occasionally. Won’t be buying a single 2k game - not that I have been purchasing any of them intentionally, gotten all of them as part of various humblebundle’s.