It is short, indeed. But for what it wants to be, it is very nice for playing in between bigger games. The puzzles are mostly logical, although rather easy. And there are nice jokes and many good ideas, for example the ghosts in the library and the setting of the underground case.
Many already wrote about the design and the narrative, which are really great. Is it also for people who are not very used to First Person Shooters? Yes, I would say. I myself just played two shooters before (I don't even like them but for westerns) and it is more than possible on "normal" (after practising with this, even on "hard"). Plenty of ammo, fast healing, no annoying escort missions, rare time-critical parts and very fair autosave system. Con: balancing is not very good - mostly it is too easy, that is when you have some cover. When you don't it can become tricky and in (for me) two places it was even a bit frustrating, although with some practice and discovering kind of a strategy it was doable without trying for days. Con: it is very simple, you don't have much options e.g. to flank the enemy and they are kind of stupid too. Con: it is rather short (but it is not expensive either, though I would have paid more for some more and bigger town levels) Three cons, but the gameplay and the presentation are big fun, so it is a recommendation for some straightforward action.