While I love "Trait" type systems (loved them in Fallout 1, 2, New Vegas and Wasteland 2)... I've never seen them implemented "well. I think if you were going to implement them at all, it should be done in a far better fashion than the four games I've mentioned.
Most problems with these Traits is that there's usually one or two obvious great ones and about 15 or 18 really terrible ones that exist purely because you want a challenge.
Just as examples, you've got things like, "Small Frame" or whatever it is in one of the Fallout games that gives you more AP for actions (or for VATS)... but you cripple much easier. So, the trade-off for being able to take more actions a turn is being crippled at pretty much every single hit you take. That doesn't exist as a "trade off" of advantage for disadvantage. Why would I ever want to be crippled every single hit just to get more actions a turn? Especially since if I wanted a lot of actions, I could just distribute my stat points towards a better build with that in mind.
You've got even worse ones in there like... forget what it's called, but you get +2 Perception (major stat, can't really be raised easily during gameplay) if you equip glasses of any kind... But, without glasses on... you suffer a -1 penalty. Seems good at first... until you realize that the best armor in the game is "Power Armor" and you cannot wear glasses under it. So, you're sacrificing the best armor in the game for a +2 Perception score.
The games are just loaded with Traits like this, and I feel like so many of them are wasted potential because of it. So many of these traits are just objectively BAD. You sometimes get ones that are just quirky (Wild Wasteland for example, or Bloody Mess), but most of the time, these are just really terrible things to take where the positive doesn't outweigh the negative. If anything, the negatives far outweigh the positives most of the time.
I think a Trait should never CRIPPLE your character. It should, however, change the way you PLAY the game. For example, I'd have changed the "Small Frame" trait to be "make you much harder to detect while sneaking", with the same trade-off... You get crippled easily, probably in a single hit. This trait makes sense, it reinforces your decision to play stealthily, because now, to not do so, results in serious damage to your character. It then turns into a playstyle choice. Sets the entire tone for you the rest of the game. I find something like that to be far more interesting than what a lot of games do now, where the negative tied to the positive is usually way out of balance or has nothing to do with the sort of playstyle taking the Trait would emphasize.
Like say... What if there were a Trait in Fallout New Vegas that made Pistols take half as much AP to fire in VATS... But, any other gun had their AP doubled in VATS to use? A "Gunslinger" Trait, maybe? Now, you're suddenly emphasizing the use of pistols, and you'll be wanting to use them quite a bit. You'll use everything else outside of vats, which means you'll have to free-aim quite a bit. Sounds like a fun trait to me, something to emphasize a specific build and discourage going too far out of line with that build.
That's what a trait should be, in my opinion. That's what it should do. It should "make a specific playstyle advantageous" while also making you do things outside that playstyle detrimental.