I, unfortunately, ended up being very disappointed by this movie, and honestly, it's a clear archetype for the typical bad sequel. It feels very much like the first one, but as someone mentioned, with the Guy Ritchie effects cranked to 11. So, what you end up with is a movie that looks incredibly stylistic, but way too often it just becomes mind numbing in its repetitiveness, and some shots were just so weirdly out of place that they immediately took me out of the experience and into a state of "what?"
But of course, had the plot been up to par, the visual thing wouldn't have been that big of an issue. Unfortunately, what we get here is a muddied and convoluted plot that goes basically nowhere. The first Sherlock Holmes had a convoluted plot too, but it unraveled its details with precision and kept the leaps of faith to a minimum, Game of Shadows however has a plot twist so out of nowhere and bizarre that it almost rivals Kingdom of the Crystal Skull.
The biggest problem however is that this movie feels like it's just one set piece after another, action upon action with little bits of plot in between; it almost feels like a video game, where the plot is the cinematic between levels. And thus, the plot there is is rather weak. I won't go into spoilers, but rest assured that after the first act, plot devices are just used to move from one action sequence to another.
Now, I've said a lot of negative things about this, but it is not a complete disaster. There are some genuinely fascinating scenes and some really great moments (my personal being when Sherlock realizes he is wrong about a bomb) and as mentioned before, some of the stylistic bits are brilliant. The big problem here is that this feels like they took everything that made the first movie good and just attempted to add a whole lot more of it, losing all of the delicate balance of the original.
As for the characters, RDJ is great in this role, he truly embodies the character and goes a bit overboard with it. For some that might now work, but there's no doubt that it's an entertaining as hell performance, much like Jack Sparrow. Unfortunately, both of these characters suffer from bad writing in their sequels and thus both of them lose a lot of their potential.
Law is a very mixed bag here. I adored him as Holmes in the first, and he brings a lot of the same quality back for the sequel, but there are just some scenes (like one when Watson is taking care of a wounded Holmes) that just seem so forced that it makes me wonder why Jude Law appears to be phoning it in so desperately.
But of course, no movie is complete without its villain, and this one could have been so much more. We are supposed to fear him, oh yes, we are told his plenty throughout the film, but yet, for all of the thing he orchestrates, he's never actually given much to do, so except for one scene, he never comes off as threatening. I understand what they're trying to go with here, and Harris is fun to watch, but Moriarty is just a badly written villain who doesn't leave very much of an impression.
If you're a Holmes fan, you're probably already going to see this one, but if you're on the fence, I'd say wait for it to be a rental. RDJ and Jude Law are still fascinating to watch together, but they suffer from a poor script. But it's still a fun movie to see, and for a night of kicking back with some friends and a few beers, it might be perfect.