Opinion is divided on this game, some love it straightaway, some give up.
It takes some getting into, as the main story line is mission based, with lots of running around what is a very large area.
However, there are plenty of optional missions, and there is a mod available which allows you to drive the vehicles - this makes it less tedious.
Graphically, it is very nice looking but needs quite a high spec PC.
If he has played Deus Ex or similar style game, then he will know what to expect, as it is not a "run and gun" game, but more realistic.
It is worth persevering with, even though it may seem hard to start with.