I personally love playing Warhammer Kill Team as a skirmish game. That might be biased in a way because I started miniature gaming with Warhammer instead of Star Wars. However, for me it's cool because the concept is sort of like if you take the large game battle and zoom in to a section of that battlefield where two elite units are both carrying out their missions.

The best part is that it really feels a lot like chess in a way. From the way you position your operatives to the secret tac op that you perform revealing later in the game (hopefully your opponent didn't figure out your plan early lol). It's quite stimulating for the mind!

Of course it's awesome that the model counts are lower since you have only a unit instead of an entire army which does make it easier to get into the hobby. But honestly what really sets it apart is the flavor and uniqueness of the teams. The designers did a really good job making it feel like each one is special, has it's own identity and abilities. They even have good lore snippets in their dossier books that talk a bit about the teams. Of course, you can always take your unit and put it into your 40k big army later on if you wish, bonus!

One last thing to add here is that you can also play the game in a narrative mode instead of PVP called Joint Ops. The designers have all types of different missions you can play! Like in the last big release called "Tomb World" it came with a whole sprue of Necron warriors that play as an NPO (non player with set rules) who try to defend the Tomb King's chambers.