While it's not a perfect game, it's better than most of the other 3D Sonic games.
The question is; is the latest entry into the franchise, Sonic Unleashed, any good? Yes, it is. It is much better than a lot of recent entries into the franchise, and I'm going to explain why.
The story of the game is nothing special, but that's unsurprising as very few Sonic games have good stories. The story goes that Sonic confronts Eggman in his latest attempt to conquer the world, and while it seems like he succeeds at first, Eggman has a trick up his sleeve which causes the Chaos Emeralds to lose their life and power, essentially causing the Earth to split into seven pieces and reawaken ANOTHER supernatural entity. As a side-effect, Sonic is turned into a werehog at night. It's nothing special and the idea of Sonic becoming a werehog is rather weird, but to be blunt, I have never played a Sonic game for it's story (barring Sonic Chronicles).
But what of the gameplay, the most important part of any game? Thankfully, it all holds up rather well, some parts moreso than others. There are two types of stages; day-time stages and night-time stages. As you can expect, day-time stages feature traditional Sonic gameplay including elements of speed and platforming. The gameplay switches between 2.5D and 3D gameplay, which is fun to play for those that prefer 2D gameplay for Sonic, while also including 3D Sonic for those that prefer that. The gameplay here is amazingly fun, and if the entire game was compromised entirely of gameplay found in the day-time stages, the game would still be just as fun as it is here.
Night-time gameplay consists of Sonic in his werehog form, which features slightly more traditional platforming gameplay with some areas of beating up enemies. The werehog isn't as fast as Sonic in his normal form, but he is able to stretch his arms and perform effective combat moves. This gameplay here is nowhere near as good as the day-time stages; the combat can get repetitive very quickly even when levelling up the werehog to introduce new combos, the levels take far too long to complete (approximately twenty minutes usually) and the camera is not perfect in a lot of instances, and are placed at awkward angles making it difficult to see what you need to do. However, these instances aren't common, and the camera is nowhere near as bad as what it was in Sonic 06.
The 360 version does include two things that were not to be found in the Wii/PS2 versions of the game; Tails flying stages and hub worlds. The Tails stages are not an altogether common occurance in the game, and focus on pressing the correct buttons in order to take out enemies flying at you. It requires the player to focus, and thus can either be challenging or not, depending on the player.
The hub worlds are smaller than the hub worlds in Sonic 06 while still remaining of a decent size for exploring, which is rather pleasant as I felt Sonic 06's hub worlds were far too big in size. Hub worlds do admittedly detract the player from getting to the next stage straight away, but it does succeed in trying to extend the game and make it last longer than what it otherwise would. There are a few framerate issues, but I don't get them enough to consider them a major problem.
The graphics are absolutely gorgeous for a Sonic game; the Hedgehog Engine is absolutely brilliant in that respect. I feel the graphics look much better than Sonic 06, and I much prefer the cartoony look compared to the realistic look 06 had. The levels look really good, even if they did not have the most fantastic of gameplay designs.
As for everything else, I will confirm that the music in this game is pretty good, and can be quite catchy on certain stages, and seem to fit the theme of each stage. The voice-acting, however, is not perfect, but I will admit to it being far better than the voice-acting in previous Sonic games. Jason Griffith now seems to be putting emotion into Sonic's voice and it works, despite not being perfect, so I'd say Sonic's voice isn't as bad as what it was previously. The new character Chip, however, has a very odd and annoying voice that just doesn't seem to fit him that good. For those that don't like the English voice-actors though, you can switch to the Japanese voice acting.
In conclusion, is this game worth getting? For the most part, yes. The werehog stages are nowhere near as good as the day-time stages and that seems to prevent the game from being as good as what it could have been. Despite that, it's still a fun game to play and is FAR, FAR better than Sonic 06. Even the werehog on it's own is better than Sonic 06 and that's saying something. I'd recommend renting this one at least.