Best in series, by far, but that's not saying much. It's a thoroughly mediocre game-for CSI fans and causal gamers only.
First, the game adds 3D perspective. You might think this would be a benefit to the game, but it's not. The game engine allows you a small amount of movement around the crime scene and other locations, but not much. For beginners and casual games (the game's obvious market) the limitations are helpful, in that it tries to structure the game a bit. For more advanced gamers, though, the limitations seem irritating.
The graphics themselves are badly dated. The resolution is low and fixed, and takes advantage of few if any advances over the past few years, which seems like a purposeful way of making the hardware requirements on the low side. Still, it would have been nice if the designers had allowed those with higher machine specs to increase the resolution or turn on some advanced effects (which would have heightened the ambience of the game a bit). But perhaps the low-resolution is best--since the textures are *incredibly* low resolution in many spots in the game. Character models are passable--if the game were three or four years old, I might say they looked ok.
Sound is good, at least when it is cast from the TV show. The voice acting for minor characters is frequently over-the-top (standard, really, in this kind of game although I don't know why).
Gameplay hasn't changed at all, really, since the previous games. It's a lot of hunting for objects, collecting evidence with various tools, and analyzing them on the correct equipment. It's all pretty straightforward, and not terribly challenging. It is possible to miss a piece of evidence and force you to start over. But that will be rare. The game is pretty easy, clues pretty obvious, and obstacles few and far between.
The cases themselves are better than those in previous games, some of which were horrid, but still not up to the quality of the television show. The game suffers from the same mediocre writing that plagues most games these days. Still, some cases are better than others, and will hold your interest long enough to play through the game (more than can be said for other games' clunky plots), though they certainly will not surprise you or offer any satisfying twists and turns.
Replay value, however, is virtually nill. Even if you don't collect every piece of evidence (not a difficult task, by the way) you probably won't be tempted to go back and find the missing pieces, mostly because they don't add anything to the story. Many are just objects with no purpose at all. The result is that the game feels like you're playing on rails. It's more like assembling a puzzle than playing a game. And that is probably what many casual gamers/CSI fans really want.
The interface remains clunky and slow. With the new 3D graphics, you're required to move in and back from lab equipment, items, locations etc. far too much. It could have been streamlined quite a bit.
As for difficulty, you won't probably need to take advantage of the game's included cheats (you can ask your CSI colleague for tips, if you must). The game does allow you to turn off various in-game helps (such as tags which notify you if you are done with an object or location, or to turn off evidence hot spots on screen). The game is more difficult that way, but not significantly so. If you're an adventure gamer by nature, this game will take you far less than ten hours to complete. Perhaps as little as six or seven, even for an average gamer like myself.
For casual gamers and CSI fans, though, the game will entertain. And though I'm not impressed with the game, I certainly can't say that I didn't enjoy it. So, despite my lack of enthusiasm, the game was solidly mediocre. I give it a qualified recommendation--if you liked the previous games, you'll like this one. If you're a casual gamer, or a CSI fan, you'll probably enjoy it. It is certainly the best in the series, but that's not saying much. Others should either wait for the bargain bin or just ignore it.