2-cost 2/2's with a command icon are always nice. Added bonus - you get to infest stuff! This is nice because it happens as a reaction to your deploying this unit, allowing you to begin your shenanigans. 

Like the Ripper Swarms, I love these guys so much I've yet to build a 'Nid deck without them

Indeed, the 'Nid card pool is so limited that these are auto-includes at the moment. It helps that they infest when deployed since so many of the other infest cards have inconvenient timing: Venomthropes during command, Virulent Spore Sacs during combat, Spore Chimney during HQ... all basically delaying quick and optimal usage of something like Digestion Pool or Spore Burst. If you want to use Pool turn 1, you need the 'Gaunts.

2-cost 2/2's with a command icon are always nice. Added bonus - you get to infest stuff! This is nice because it happens as a reaction to your deploying this unit, allowing you to begin your shenanigans. 

 

Like the Ripper Swarms, I love these guys so much I've yet to build a 'Nid deck without them

I dunno, compare them with almost every other 2 cost with 1 command in the game, and they look seriously underpowered to me. All depends how much mileage we can get from infestation, I guess.

I'd run them alongside a Synapse Unit that mentions infestation in its trigger, but probably not otherwise. That's in the long term, of course. Right now, choices are kind of forced by Tyranid command deficiencies.

I think that we can say with certainty that infestation is essential for getting the most out of Tyranids. Let's break it down by card type:

Synapse: It greatly improves both Blazing Zoanthrope and Tervigon, pushing both of them to useful, rather than being sub-optimal synapse coices (behind Lictor and Warrior Brood).

Command: It makes Toxic Venomthrope one of the best cappers in the game, being a 2 command 0/2 for 2, who now gives +1R.

Units: Although I think it is regarding units that infestation is currently weakest, but it super-powers Gargoyles and Shrieking Harpy - two of the best units in the Nids unit pool currently.

Attachments: Scratch above, as infestation really gives no benefits re: attachments.

Supports: Digestion pool is of course amazing with infested planets.

Events: It certainly makes Dark Cunning a great event, but it is necessary to empower spore burst, which is really the best non-signature event for Nids.

So infestation provides some really powerful effects, and it is unambiguously the case that Scything Hormagaunts is the most efficient way to infest a planet. It is 1C2R to infest a planet, but you get a 1/2/2 out of it to boot! I think that this is a much more welcome card than Spore Chimney and Predation, and it is more flexible as a method of infestation than Toxic Venomthrope, because Hormagaunts are point and click.

So although it's not as directly flashy an ability than other 1/2/2 units, I think that it is ultimately more effective overall.

Solid unit and easy infestation. Great.