This card is quite bad. It might seem superficially attractive, as it's a skill card you can use to boost any important test, and then maybe get it back to boost another important test later.
The problem is the "succeed by 3 or more" requirement. This means that if you did well enough to get Opportunist back, Opportunist did not make a difference on the test. There are several Rogue cards that care if you succeed by 2 or more (Quick Thinking, Switchblade, .41 Derringer, etc.) but there are none except Opportunist that care if you succeed by 3 or more. So if you play Opportunist and succeed by 3+, then you get it back, but it didn't make any difference. If you succeed by less than 3, maybe it did make a difference, but then you lose Opportunist. See the problem? Even though it looks like you can use this card over and over, it actually can only help you a maximum of once per game, because once it makes a difference, it's discarded.
You might say that the point of Opportunist is that it won't be wasted if you happen to get a really good result, whereas something like Unexpected Courage would be. But in actuality, there are virtually zero tests where a) +1 makes a large difference to your odds of success and b) you nonetheless have decent odds of succeeding by 3+. The math just doesn't work out.
Moreover, there's always a chance that you fail the skill test (or succeed by 1, or succeed by 2 on a skill test that doesn't care how much you succeed by), in which case you lose Opportunist having gotten no benefit at all. Of course, every time you commit any skill card there's a chance it will be wasted. But other skill cards either do more to help you pass the test than Opportunist's rather measly +1, or grant a more useful reward for success.
Quick Thinking is a similar card that is much more useful. It has a better benefit--an extra action is better than just getting Opportunist back in your hand. (Consider that you could use that action to draw a card, or you could use it to fight, move, evade, or whatever's useful at the moment.) Quick Thinking can be used to boost other investigators, whereas Opportunist cannot. Finally, it has a lower activation threshold (2 instead of 3.) Unexpected Courage is a much-superior card, too.
Nonetheless, in the days when the Rogue card pool was thin, Opportunist would see some play, just because the wild icon was helpful. But with a recent influx of quality Rogue cards like Quick Thinking, Think on Your Feet, and Lone Wolf, Rogues no longer need to fill out their decks with chaff like this. Opportunist can be safely set aside.