Realistic but uninspiring mechanics
Velvet Assassin is a stealth game set in World War II. You play as Violette Summer, a British spy operating within enemy lines. As the theme tries to stick to realism, and the game is set in the past (unlike, say Deus Ex), you do not get fancy abilities to help you -- apart from morphine, that is.
Using morphine stops rest of the world for a duration, allowing you to traverse unnoticed and/or safely take out someone. The reasoning behind this, obviously not realistic feature, seems to be that those are times when Violette is given the drug in the present time and her dreams -- that tell the game's story in flashbacks -- get foggier and less accurate. This also (sort of) explains why her attire changes to a nightgown when the ability is active.
The fact that morphine can no longer be found in the last two chapters, which take place after Violette has woken up from her coma, reinforces this theory of mine. (Apparently no proper clothes can be found anymore either.) Thus you better have put all points intended to upgrading the ability before that happens.
Stealth with poor shooting
Killing enemies (no non-lethal way in this one) happens mainly with stealth kills. There are quite a few different animations for those, probably close to the number of what Deus Ex: Human Revolution has in total. I think the most brutal one -- a stab to the chest, followed by multiple more once the enemy is on the ground -- was on purpose saved to be possible to happen only in the final chapters as the nightgown creates quite a contrast to the violence. I think for immersion purposes the pistol kills should have left out, though, as 1) they do not use ammo, and 2) are far more silent than actually firing a silenced pistol in the game.
Very much like in Mirror's Edge, gunplay in Velvet Assassin is clumsy. You move slowly with a weapon drawn and there is no aiming down sights with the exception of the sniper rifle that has a scope. Thus you are stuck with hipfire and the inaccurate reticle. It is not of the circle type I hate, but still, one that shows the actual pixel you are pointing would have been so much better. I do not understand why putting such a thing in a game is so damn difficult.
The checkpoint saving system can get really annoying. Especially in a game of this genre saving whenever you want should without a doubt be possible. There is simply too much potential for frustration for a stealth perfectionist like me. My 16-hours playthrough was well above the usual 10 hours it apparently takes to beat this game.
I also did not appreciate how enemies going to the location you whistled at, always have their upper bodies trying to face your current location as if they knew you were there. It was rather unnerving. They tend to have a bit random detection level at times, too. An enemy going right past you will see you even in shadows but at one time I was holding a body right in front of one and he turned away without noticing a thing.
Stable but requires effort to get running
The game has a "PhysX by nVidia" intro clip and I think it is somewhat ironic that the physics engine in question is the very reason one might not be able to play Velvet Assassin out of the box, and instead meets an error message when trying to start it. The game apparently requires version 2.7.2 of PhysX that is removed by newer installations of it. Someone is hosting the folder in his dropbox at the game's Steam forums, and I think the PC gaming wiki article had a direct link to the zip as well.
On Windows 8+ the game apparently also requires some additional trickery to run on fullscreen. I did not have that issue as I played it on my older Windows 7 machine. The game's system requirements did not seem that high but I was getting 20 FPS in-game. I lowered the settings to minimum but probably could have upped them a bit (at least anti-aliasing and shader quality) as the performance got noticeably better once I got out of the starting area. The lack of mouse control in the menus also speaks of laziness.
Mostly uninspiring visuals
The scenery in the game is fairly boring. You either get maps basking in warm yellow light or blueish night scenes. More variation would have helped. There did not seem to be that many different music tracks either but since consist largely of random sounds, they did not get too repetitive. Melinda Cohen gave Violette a pleasant voice. The NPCs also speak either German or French, which I think was neat.
Velvet Assassin was a pretty plain, barebones experience. The next game on my list evidently has sneaking as well but that does not seem to be its only feature. I am very much looking forward to playing it.