95% of my games are played in the early-mid WOTC era in 100pt so I'm probably not as relevant, but here's my play group's main NPEs
-Override: My acquisition of an Elite Rebel Commando into our collection led to a lot of frustrated players. Its kinda sad seeing Vader rendered useless by a non-unique with override. I ran into this to a greater extent during the vassal tourney, not being able to attack because of door control wasn't great, but I guess more ugnaughts fixes that problem.
-Getting attacked but not being able to attack back: Cloaked, stealth, molecular shield, mobile attack. Most players are annoyed when they have to charge pieces into the open to try and retaliate against these guys. I can tell this isn't as big a deal in today's game though.
-Strafe: We played 1 game with the basilisk war droid. There was a lot of yelling and rule checking when I dropped 30's all over the place and didn't get shot at. That game didn't finish, never played with it again.

Again, this is all old stuff probably and my small collection pool probably doesn't help either. We usually have far more positive experiences than negative ones anyways.

I also agree with the aforementioned outactivation issue.

NPEs can be broadly categorized as:

Non-engagement: These techniques gain an advantage by not allowing the opponent to attack, or at least not attack anything worthwhile.
Lockout
Out-activate and smash (especially with initiative control)
Activation control
Attack+swap (leaving a Brute behind)
Deep strike with a throw-away piece (e.g. Repulsor Sled/Snowtrooper)
High-speed Strafe
Cloaked/super-stealth
Diplomat


Denial: It's annoying when one squad tells your squad, "You cannot do the cool thing you designed your squad to do."
Ysalamiri/Vong
Disruptive/ABM
Squad Discipline (giving Disruptive a taste of its own medicine)


Punishment for doing what you're supposed to do: Killing the other squad is sort of the point of the game.
Self-destruct
Death shots


Inelegance/Tediousness: Some things tend to slow the game down... high activations, counting squares, rolling dice
High activations (regardless of engagement)
Tank squads (with lots of dice rolls)
Massive movement breakers


Play Style: If you favor a particular play style, your bad match-up/auto-loss will likely be an NPE for you.
Extreme Rock (if you like Scissors squads)
Extreme Paper (if you like Rock squads) - Rock is the most popular squad type so this causes an NPE for more people
Extreme Scissors (if you like Paper squads)



Notice how appropriately NPE Extreme is named. It includes tons of the above: an Extreme squad with tediously high activations, self-destruct, strafe with high speed, activation control + initiative control, and lots of Override.



Some of the pieces that get the most complaints combine multiple NPEs into one.

Lancer: Almost automatically creates an Extreme Scissors squad with a tedious massive movement breaker and the non-engagement of high-speed Strafe.
Daala: Often an Extreme Paper squad with a tediously high number of activations, along with non-engagement in the form of a deep strike with a throw-away piece.
Klatooinian Assassin: Non-engagement of Cloaked plus the punishment of self-destruct

Thanks. I voted for Cloaked/Self-Destruct because it gives you the double-whammy of non-engagement plus punishment if you do engage.

Have to give it to Bastilla. Single-handedly made commander effects not as good and sparked a whole new special ability route just to give the other factions a chance. Crippling commanders ironically has become a great counter to other problems like Daala squads

It should be noted that daala squads also sport out activate and smash versions.

I haven't personally played against Deathshots yet, but I can imagine that's got to be one of the hardest NPE's in the game.

Awhile ago I would've said Lancers-strafe is the NPE I most dislike, but with the pieces we have been getting lately like the Buzz droids, I feel safer. That and most people are sick of playing it. Right now I dislike plying against high activation squads that force me to play aggressively when I don't want to. (either that or far more defensively)

Door control I can deal with and Tank Squads are fun to play with and against IMO.
Bastila's ABM and Disruptive can be a huge pain, but I don't think it's the worst.

So I'm going with Out Act and Smash! And Non-engagement types which I would say includes Daala.

I think poor sportsmanship by your opponent should make the list.

Agreed. My biggest NPE overall is when my opponent just folds and suicides the moment they are at a disadvantage. It makes the whole game feel worthless.

Even worse, they run, hide, lock doors, stall... to deny you a full victory.

Typical! Lol