Denise Crosby was just incredibly beautiful and she could act. By the end of Season One of TNG, though, Yar had been reduced to eyecandy, hanging in the back, like Uhura had been in TOS. She was given trite, almost unnecessary dialogue like "Torpedoes firing, Captain." "Hailing frequencies open, captain." Essentially, Yar lost her importance to the series, and leaving made perfect sense, if she didn't have enough clout to change things, which she apparently didn't.
Except for Sela's rather unorthodoxed origins, she wasn't a particularly engaging character. Denise Crosby also didn't seem to ever get a handle on playing her, either. She imparted a sort of ice queen demeaner to the character, a sort of bitchiness, but it was never convincing enough. It's such a shame because I feel that Denise Crosby was important to STAR TREK's legacy. She helped give TNG its own identity and that wasn't easy, when they were still in STARFLEET, still using a spaceship called ENTERPRISE and still had a young studd in a command position, onboard. But Sela was not the answer to how she'd been wronged, earlier.
Yar shouldn't have been killed off is what should've happened. She should've been offered a unique opportunity and transferred off the ship. Or maybe even resigned to do something important, but oh, no ... Denise Crosby DARED tell The Great Bird of the Galaxy that STAR TREK wasn't good enough for her, so he got his little revenges in, as he may. And I don't think this served the series, or the franchise, at all ...