It is almost certainly not a fair spell, in the right scenario, and when used cleverly.
I have reduced a boss encounter to a trivial difficulty using this spell. The boss in question was a 9th-level spell caster, who tried to get both a 7th- and a 9th- level spell off against a bunch of level 7 PCs.
With 20 Cha, advantage on the check, the Lucky feat, and Bend Luck at the ready should I need any of them, I was rather secure in the knowledge that I could counter any spell the mage threw at us.
In fact, the average roll for the particular combination of abilities above gives an average of 23 to the roll, and a 92% chance to roll a 12 before modifiers. To counter a 9th-level spell this way, my odds are 85%: good enough for me to risk it. Furthermore, Subtle Spell on that Counterspell also prevented the opposing mage from countering my counterspell, as @keithcurtis warns might be possible.
Counterspell uses better action economy
By using your reaction to deny them their action, you are using the action economy more efficiently than the monsters. And any advantage in using the action economy is huge in this edition. That is why Quickened Spell and Twinned Spell are so good. And this is another reason why Counterspell is unfair.
What I lost
That said, this character was weak in many other things and could not dole out massive damage. He was not physically resilient in terms of HP. He was built to stop mages from harming him, but he couldn't kill them. He had to rely on his party for that.
Counterspell also eats your reaction. So in an airborne battle, any round you use Counterspell is also a round you can't use Feather Fall. In a battle with melee components, you can't use Shield if you're keeping your Counterspell at the ready. As a wizard, you also have access to Absorb Elements, so in a battle where more elemental themed magics are used, you can't Counterspell and have protection against the elements in the same round.
Finally, most of the time, they wouldn't be dealing with magic users. And so Counterspell was mostly unused. Instead, it took up space in my spells known (and for your abjuration wizard, your prepared spells).
Given all these trade offs for the benefits, I'd say Counterspell can be considererd a fair spell.