I write this as someone who considers himself a dedicated fan of Freeman's Mind. I realize that I might be in the minority here, but I'm not really a fan of when Gordon goes "off-script" and does things that aren't usually possible in the game.
As I wrote on my blog, if I were to pitch Freeman's Mind to a prospective viewer, I would say this: "Hey, you know all that time you were playing as this game character and going through this adventure? Ever wanted to know what was really going through that character's mind all that time? Here it is!" That's one of the core draws of the series, and it only works when said character is only doing things that the player could actually do.
It's understandable if you take the occasional shortcut to skip puzzles and other portions of the game that would be boring in a Freeman's Mind video, but adding in new areas of the game world have little point. It lacks the aforementioned appeal of riffs on material the games' players have experienced.
If you wanted to, you could put something really wacky in a new area, like a pyramid of watermelons surrounded by dead headcrabs who seem to have been worshiping it. It would be funny, perhaps, but it wouldn't fit in with the established style of humor of Freeman's Mind.
Freeman's Mind works best when it works within the constraints of playing through the games while staying in character as its version of Gordon. This occasionally leads to another entertaining aspect of the series: Your being challenged to go through the motions of Gordon while staying true to the character you have developed for him. You can't canonically attack the vortigaunt in the rail car, so how will you explain why your version of Gordon doesn't attack him? Modding the game so that Gordon does shoot him feels like kind of a cheat.
Continuing from my comparison of Freeman's Mind to Mystery Science Theater 3000, I am reminded one controversial point in the latter. In a very early episode, they manipulated the movie in a way that went beyond what their audience characters would be able to do. For example, the silhouette of Joel put his hand over the mouth of a singing woman in the movie, and her voice was non-diegetically muted. A writer for the show apologized for this in the episode guide, acknowledging that it violated the show's unwritten rules.
That's my opinion, anyway. Take it or leave it. Thank you.