I like the CoD MW series for Single Player because you can always do 1 run in Normal Mode, then another in the hardest level. Once you are done, you can always look forward to the Solo Play Missions... plenty of fun all around.
Watch dogs... I was unable to find anything for the PC so I don't know if it will come to PC (didn't really waste much time looking either). Then again, it is a Ubisoft game so expect, lots and lots of glitches, errors, bad porting, etc. The pisser is that you know the game has lots and lots of potential but even after many patches, the game will still suck before of what I mentioned before.
GTA V... played the first one, liked it but never played the others as I always heard they had issues and were heavy into cpu and gpu and my rig has always been lower-end so, unless you have a brute force rig, expect to play it with minimum settings and at very low fps.
So... win win for CoD