I did too - but I had just seen the Firefly episode.
Castle seemed hesitant to take the gun. Was this the first time he carried one in the show?
His reaction was very good. I could imagine him thinking, “wait a minute! I’m a writer and not a real cop”. 
Yes, the “aiming for his head” thing was great…but I always considered the Firefly reference to be a nod to “Rustler’s Rhapsody”
He’s been at the shooting range at least once, and IIRC he hustled Beckett. He acted like a newbie with the weapon, got her to agree to a bet, and promptly put two bullets dead into the target. I don’t remember the episode, just the scene. Pretty sure this was his first time with a weapon in a live situation, though. Becekett wouldn’t trust him with one before.
The technology thing was fantastical enough for me to notice it too, and my disbelief is usually very easy to suspend. I’m kind of miffed that when they had the heat signatures up on the screen, nobody pointed out neither person was moving. Even the top-down view was clearly pretty accurate, and nobody sits that still. The literary aspect was strong, but together with the lack of motion it should have been downright compelling.
Despite that, it was a great episode. It stuck to Castle’s formula in some ways but broke it in others, just enough for me to be uncertain of how it would play out. Even after they’d made Dunn, I kept expecting a double-cross from one of the Feds.
One thing I noticed was that, just as Dunn refused to acknowledge Beckett as Beckett, he seemed to refuse to acknowledge Castle’s presence. He was so fixated on “Nikki” that Castle seemed not to figure into his world at all, which is unusual considering Castle doesn’t exactly hide his presence at crime scenes. I guess, for as smart as Dunn was, his psychosis gave him that fatal flaw. Had he been a little more grounded in reality and understood how a writer working with the cops would affect their behavior, and especially Beckett’s, he’d never have been caught unaware.
You’re not counting Principal Wood (D. B. Woodside)?
Pazu- Or Mr. Trick, either! He was a fun villain.