Absolutely agree that "Lo-Fi" was a magnificent finale, one of the show's best season finales along with "The Fisher King Part 1". In fact, it is one of the two best episodes of Season 3 along with "Elephat's Memory" (one of the show's most poignant episodes).
Don't agree personally that Season 3 has been mediocre. Sure, the episodes between "Doubt" and "Children of the Dark" suffered from having to work around the abrupt departure of Gideon, but they did do a much better job than expected considering the circumstances. Rossi's first appearance in "About Face" was also a little shaky and the team dynamic was understandably awkward on-screen and perhaps off-screen too, but again it could have been worse considering.
However, to me there were some very good episodes indeed, "Children of the Dark" and "Seven Seconds" was when Season 3 started to get great, and while not everybody liked "True Night" there was a huge amount to like about that episode as well. Remember liking "3rd Life" very much too. While there were a handful of very good to great episodes, the two outstanding ones were "Elephant's Memory" and "Lo-Fi".
For starters, "Lo-Fi" is the most tense and most unpredictable Season 3 episode. The tension and suspense piles on and on to a terrifying degree while there are plenty of twists, turns and quite ingenious red herrings, the beginning setting the tone of the episode superbly. The killings are too some of the show's boldest and most risky, and "Lo-Fi" not once loses sight or forgets what makes 'Criminal Minds' such a good show a good deal of the time (something that the mostly very disappointing Season 11 made the inexplicable mistake of doing). The pacing is very quick but just about avoids being rushed, while the cliff-hanger ending is pretty frightening.
"Lo-Fi" is as always an incredibly well-made episode, a lot of style but an equal amount of class and grit. There is some very good choice of background music as well, atmospheric and with the occasional air of melancholy. The script is taut and smart, with enough tension to bite the nails and great team dynamic, characterisation throughout the episode is simply excellent and some of the best of the season along with "Seven Seconds" and "Elephant's Memory".
The acting is very good from all involved, lead and supporting. Hard to decide who stood out because absolutely nobody was bad.
Overall, a brilliant episode and one of the best of the episode. Need to re-watch the Season 4 opener "Mayhem", but it has a huge amount to live up to to be as good as this. 10/10 Bethany Cox