Terran:

Hellion: Annoying. I preferred the Firebat, but oh well.

Siege Tank: SIEGE SIEGE SIEGE SIEGE SIEGE SIEGE SIEGE SIEGE

Zerg:

Queen: <3. Spawn Larvae and Creep Tumor are beautiful. I try to have one per hatchery.

Baneling: Fun enough, but hyper-fragile. I only ever use them to crack open turtles.

Nydus: So. Much. Fun.

Mutalisks: Way too expensive for how bad they are. This is the problem with Zerg air. You have to mass for it to be effective at all, meaning that you have to run a huge gamble teching towards air for a possible payoff of general decency.

Corrupters: I don't want to talk about it. The worst unit in Brood War makes a re-appearance. Ugh.

Brood Lords: I like the Guardian's remake. But it takes about twice as long to get a Brood Lord as it does a Banshee. I know Banshees are weaker, but Zerg air is useless without this unit. A Hive really shouldn't be necessary for a Greater Spire.

Ultralisks: <3
Protoss

Void Ray: ...I don't want to talk about it.