I have given this game a fair chance (BTW, it isn't like Halo) and I think it's a bit rubbish. Certainly nowhere near the same class as the first. The framerate is very choppy meaning that FPS portions of the game play very poorly. The "stealth weapons" are nearly useless; the stunprod taking 5 or 6 goes to take down an enemy. Therefore, the game mechanics make stealth gameplay unnecessarily hard and the framerate makes the FPS gameplay poor. My advice is to either wait until a decent PC patch is released and play it on PC (if possible) or forget it altogether.
Certainly if you are looking, in terms of quality, for a Halo replacement then this isn't in the same league (and I wan't that taken with Halo to start with).
Russell