I'm looking for a decent open world game for the PC. I loved Just Cause 2 and the GTA franchise. Dead Island 2 was also a good play, but I'm a bit too jumpy to make myself go through another one of those again! I would like a mix of driving different vehicles and first person shooter style, so things like Assassins Creed & Elder Scrolls I know I won't like. So, looking around, I can see Sleeping Dogs for a £5 off Stream and Far Cry 3 (which I don't think has any vehicles in it). Which is the one to get from either of those?
Sleeping Dogs is a rather hard game. I have it on the PS3 and still near the start as there's this part that I can't seem to pass. It's first and foremost a martial-arts brawler, so it throws you head-on into trading blows with a number of opponents. I'm in it early enough that I haven't even gotten into any shooting yet, but I hear it's more of a secondary thing. The fighting takes more after the Batman games, but it's rather unforgiving at times. I had to give up on it because I just found it too difficult to be enjoyable.
If you enjoyed GTA, the Saints Row series might suit you. (Not an FPS though) For an FPS with some vehicular mayhem, Farcry 1 and Crysis 1 might also suit. How open world they are is up for debate though. (I haven't played FC3 so can't comment on that one and I can't remember if they have vehicles in Farcry 2)
I got Far Cry 3 from the fall Steam sale and found the gameplay to be horribly repetitious, so I DON'T recommend it. I DO however recommend Far Cry 3: Blood Dragon. Same type of gameplay as the base game, but nowhere near as long, so it cuts out all the tedium and doesn't overstay its welcome, and its riff on 80's action/scifi is absolutely hilarious. I also heartily recommend the Saints Row games.
Sleeping Dogs was alot of fun. I would highly recommend it, if only for its unique feel and atmosphere.
I can't offer you any suggestions because I'm in the same boat. I'm going to hang around and hope a suggestion catches my eye. Although, unlike you, I don't care for GTA or Just Cause 2. Those games were a little too large and open-ended for my tastes. I'd prefer something a bit smaller and with a tighter focus, but still an open world game.
The Ur-Quan Masters HD (formerly known as Star Control 2) It's an old classic from the 386 processor days, but you can download an open-source version that will run on modern computers. Totally open-world and features one of the best sci-fi storylines ever.