*WARNING! ACHTUNG! SPOILERS! SPOILER ALERT*
First of all, the idea of a few fans of the Broken Sword series to make a game of their own is excellent. It shows a lot of appreciation to the original, and of course, dedication. Unfortunately, it also sets the expectations a bit low, as with many fan-based projects of the past.
*WARNING! SPOILER ALERT!*
Considering all that, Broken Sword 2.5 is overall so good and so well made, that it could easily have been a commercial title (in theory). The hand-drawn graphics are awesome, including the characters, despite some obvious differences between the original ones (George, Nico, etc) and some newly introduced. The story is exceptionally written, very nicely delivered to the player, and the puzzles are very good as well. Not too hard, not too easy. Even harder would be great, but that's too subjective anyway.
*WARNING! SPOILER ALERT!*
However, there were also a few drawbacks with the plot. One, the reintroduction of two previously dead characters, Guido and Khan. The player is presented with strange and dubious reasons to explain how they survived. The reason provided for Guido was simple, direct and maybe OK, considering he could have taken cover at the last minute before the explosion shown at the finale of Broken Sword 1. Adding a few scars to his appearance would also help a lot. On the other side, Khan had been seen dead and had his body searched by the player in that game, and his explanation about being a "master of illusion" does seem a bit plausible, but is still too far-fetched. Also, let's not forget an easter egg in Broken Sword 2 involving his ghost, directly affirming his death. Additionally, the entire conversation about how he supposedly never intended to kill George was way too silly and childish. These "plot holes" are made even worse by the fact that Khan doesn't really contribute to the story and could have easily not existed at all in Broken Sword 2.5.
The second problem concerns the voice acting of George in the English version only. I do not speak German, but I am willing to believe the voice acting in the German version was perfect. In the English version however, amidst excellent voice acting for other characters, and amazing similarity to the original voices, George's voice is flat, emotionless, and it's really obvious that someone who might not have known too much about the series read some phrases flatly in front of a microphone. Again, considering this is not a commercial release, but has a very limited budget based on donations etc, that is still perfectly OK and understandable. What is appalling and disturbing however is the awful mispronounciation of certain place names from the original games, such as Montfauçon, Vasconcellos, other french phrases etc.. It would be expected by hardcore fans who made all this effort for EIGHT YEARS, and produced something so awesome, to at least make sure that a handful of names are pronounced properly in English.
Overall, despite the above problems, I'd rate Broken Sword 2.5: The Return of the Templars with a 90%.