Why HPL2?

[Googolplex]

HPL2 is an excellent engine for horror games that will also handle very accurate physics.
I found HPL1 engine of Penumbra a bit more realistic, but in general HPL2 is good enough for some further titles.
I don't know how much the improvement of HPL3, but I think they are still working on that engine, so that thechineseroom need to use the final HPL2 engine and they modified it to HPL2.1.

If the further upcoming games would be same good as Amnesia or Penumbra, it's no matter what engine they use, I'm totally satisfied to HPL1 engine.