If you've already played the game on the Nintendo 3DS, it's unlikely that you'll find anything in the game's PC port that would justify a second purchase of the game. Unless you're feeling particularly supportive of Image & Form, and/or you despised a particularly aspect of the game's user interface on the 3DS, save your cash and play your existing copy of SteamWorld Dig.
Everything about Diablo 3: Reaper of Souls leaves me wanting to more, despite the fact that I've already cleared the campaign on multiple occasions, and I wouldn't be shocked if I've got a full roster of level 70 characters by the time the year comes to a close. It's been a long time since I enjoyed a hack-and-slash title as much as I'm enjoying Diablo 3: Reaper of Souls, and I plan to milk that for all it's worth. I suggest you do the same.
I have very little doubt that there's a bright future ahead for Watch Dogs, at least at the cash register, and I'm sure I'll be fairly hyped for whatever comes next in the series. But, it's hard to recommend Watch Dogs to anyone that isn't absolutely ravenous for a new PS4 or Xbox One game to play.