Hey,

For third person, I strongly suggest you have a look at those three games

1.       Metal Gear Solid V

2.       The Last of Us

3.       Deux Ex

They all have some stealth gameplay that could give you a good sense of what a third person stealth game should and would look like.

For 2D stealth game, Mark of The Ninja and Invisible inc (Both made by Klei Entertainment) are probably your best reference. What I like about 2D stealth game is that they will present fewer mechanics to the player and focus on their flexibility and reusability. 3D stealth game tends to give the player “many options to play the game your way” which is hard to balance and to master. You can easily get lost in too many mechanics like Assassin Creed: Syndicate.

Some people might think FPS his bad for stealth but I tend to disagree I think its even better than third person. Third person his generally use in adventure type game with stealth component. Stealth focused game in 3D will more than often go for FPS point of view. Have a look at Dishonored one of the most regarded stealth game of our generation.

TLDR:

2D stealth game, keep it simple and go for few mechanics that you can recycled in many ways.

3D stealth game, FPS for stealth focused game third person for a game mixing two or more types of game. Dishonored