Penumbra Prequel made in Amnesia

[Bridge]

The problem is, that Amnesia has flashbacks which will pull you out of the immersion […]

They do no such thing. They make you even more immersed by emotionally connecting you to the scenery and plot. Instead of an 8 hour walk with occasional monster encounters you now have an exciting story with a varied cast of characters (some more superfluous than others (I would have cut both Agrippa and Weyer)). Personally I think it's genius and a good example of making the most out of a simple premise.