One drastic change is that locations in The Testament of Sherlock Holmes are full 3D environments where you control Holmes or Dr. Watson in a first-person or third-person style much like you would find in most shooters. The only difference here is that instead of firing on enemies, you are selecting points-of-interest to look at or apply inventory items to.
The Testament of Sherlock Holmes seems to boasts a pretty solid graphics engine featuring highly-detailed characters, textures and lighting that should make most gamers happy. I was especially impressed by the designs of Holmes and Watson. Both fit my mental image of the duo to a tee. Holmes reminds me a lot of Jeremy Brett's portrayal of the role of Holmes in the 10-year long British TV series that started in 1984. While Basil Rathbone might be considered the most well known Holmes, Brett is the one I grew up with, much like David Suchet as Poirot
While you can probably point to several other games on the Xbox 360 with more realistic graphics, considering Frogwares' previous games, The Testament of Sherlock Holmes is a pretty impressive jump forward for the company.
Audio is another place where The Testament of Sherlock Holmes does a good job. Both Watson and Holmes sound right and their lines are delivered well. The only times I had a problem with the dialogue was when the one-off comments made by one of the characters when looking at an item didn't fit the mood of the rest of the scene.This was typically one of the characters acting really excited by the fact that the item I looked at was there, even though that didn't have any real bearing on the investigation. I don't know if it was just a matter of the wrong sound clip being used in the final product or there was confusion in the recording booth as to what the situation called for. Either way, it was odd whenever it happened.
Outside of those occasions though, everything from the background music to the ambient sounds fit the feel of the game pretty well.