RPG... which do you mean? There's "RPG" like Final Fantasy and Fire Emblem, and then there's "RPG" like The Elder Scrolls and Fallout.
Since you like Stealth, Rocksteady's Batman games seem to be at the top of the line. There's also Thief, Splinter Cell, and Metal Gear. And I really don't know all that much about them, so you may need to look around, yourself.
"Free Roam"... You want games that let you traverse large, open landscapes. Is that it?
In that case, I can name a few franchises that do this in different genres.
For platformers, I would strongly recommend Banjo-Kazooie, Banjo-Tooie, and Donkey Kong 64 for the Nintendo 64. If you've even heard of Super Mario 64, you should know that these are within the same "Collecthon" genre, except that the three of them are all leagues better than Super Mario 64. They're huge, colorful, try to keep doing something different all the time, are loaded with hidden goodies, and are some of the mos hilarious games I've ever played. The best of these is Banjo-Kazooie for me.
If sandbox games are your thing, I've been playing the grandfather of sandbox lately: Grand Theft Auto III. I'm not familiar with the series, as this is the only installment I've played, though I've been told that the best GTA title is San Andreas. I was hesitant to play at first, considering these games are about street crime. But then, I discovered that Grand Theft Auto is downright bonkers. So, no worries about it being a proper crime simulator. However, my two favorites in the sandbox genre currently remain to be inFAMOUS and [Prototype]. Why? Because, when it comes to traveling through sandbox environments, there's no better way for me to do it that when I have super powers. inFAMOUS has a moral choice system, and [Prototype] over-the-top explosive. They're both very good, but virtually nothing alike. Just sandbox games with super powers. The Red Dead series seems pretty cool, though I haven't gotten my hands on them. Contrary to popular belief, Redemption is not the first game. Red Dead Revolver was released on the PlayStation 2 and X-Box. My favorite thus far would have to be inFAMOUS.
But, there's still a little bit more out there. First-Person Shooters. There's ID software's newest IP, Rage. It's pretty open, and has got a very immerse, living world. Plus, it's got vehicle combat. And it's a heck of a lot better than the usual vehicle sections you find in today's FPSes. Ghost Recon is pretty cool, and one of the most realistic shooters I've ever seen. The only one I can think of that's even more so is ARMA. Though, I'm not certain if it's open-world or not. I know Far Cry is. It's on an island, and you can even build your own levels or something. Plus, it's got some of the greatest AI and weather condition systems I've ever seen in the last generation. But, what's easily the best for me to recommend in open-world first-person shooters has got to be the one and only... Serious Sam.
So, I would most recommend...
Banjo-Kazooie
https://www.youtube.com/watch?v=3bxHbFMZhm0
https://www.youtube.com/watch?v=O8HBZzHcvh4
inFAMOUS
https://www.youtube.com/watch?v=S-NBsSfxH30
https://www.youtube.com/watch?v=uAr3vkjip3E
Serious Sam
https://www.youtube.com/watch?v=JTbwOukQlDY
https://www.youtube.com/watch?v=mQGO46QGlbk
Batman
https://www.youtube.com/watch?v=dErlfFt1mUc
https://www.youtube.com/watch?v=944Ty9YpjEs