Since I just finished Requiem, I'll ressuscitate this post for the second time!
I enjoyed Requiem, too. The most fun part of Penumbra/Amnesia for me is exploration and puzzle solving, so it was nice. However, as we all known from Overture's combat and the "run - make wrong random choice - die - repeat 10 times" parts, the engine is just bad for action. You cannot enjoy properly a plataform puzzle when you can't see your feet!
I think what bothered people the most was the quite non-existant story. The few remains of a plot are bad not so good, but not horrible, too. With the illogical goal of chasing "keys", you can tell from the beggining that this is going to be an old fale of "it's a dream" or "this is all in my mind". But the very end is the worst possible...
Seriously, after killing mutant animals and hiding from aliens hybrids for two games, all comes to an end with some dude sneaking behind you and knocking you down with a pipe or whatever? and you only choice is to let your mind go or keep "living" inside of it? Geez, that's what I call an anti-climax...
RenKalan: I actually loved the whole series!
Now, if you have the Amnesia: The Dark Descent game you can play two great total conversion mods,
Penumbra: Necrologue and its sequel
Penumbra: Twilight Of The Archaic. The first one starts right where Penumbra: Requiem ended.
You should give it a try!
But I'll give those mods a try. They seem to be very well-mad and hopefully have a good plot!