Anyone looking for a unique and intriguing, yet somewhat flawed, game should definitely pick up Second Sight.
In terms of comparision, Psi Ops is an adrenaline fueled third person shooter with some highly fun and addictive psychic powers, on the other hand Second Sight is an average stealth shooter with some exceptionally (yet equally) cool and addictive psychic powers.
Anyway, the PC version of S.S. has a few key differences, in the visuals dept. the game includes sharper textures, cleaner graphics and interfaces and most of all the option to choose higher resolutions. S.S., being the first PC game from developer Free Radical, has a pretty good control scheme, though the camera control could've been more polished. S.S. has a better story than Psi-Ops and the character development is also much better, voice acting is a bit complicated, sometimes decent and sometimes exemplary.
So it's up to you to use YOUR psychic powers and choose wisely between P.O. and S.S. From my point of view buy both as they are two distinct games in almost all manner.