It works... but not always.
Let it never be said that developer Vicarious Visions lacks innovation and ambition: These folks have often tried to push the limit of portable hardware, first with Tony Hawk's Pro Skater 2 on the Gameboy Advance and then in trying to craft a 60-frames-per-second 3D graphics engine for Spider Man 2 DS on the handheld's launch day.
With the new guitar grip, Vicarious Visions has made the unthinkable happen. Guitar Hero: On Tour IS Guitar Hero on your DS. It's not some cut-down version where you play it with your thumbs, like on a mobile phone, or with the face buttons and d-pad. It's Guitar Hero, in the flesh, with one hand curled up as if its fingers were getting ready to dance across a fretboard, and your other hand ready to pick and strum at a moment's notice.
There are problems, sadly. The issues with this game are largely mechanical, as opposed to with the content. The guitar grip is prone to slipping out of the Gameboy Advance slot during intense play, forcing players to reboot the entire system. It's also quite unwieldy -- and even more prone to slipping out -- for those with large hands. It takes longer to get to a comfortable angle with this peripheral, since your hand is tied down by the unit's strap.
Furthermore, though the strumming "feels" somewhat like strumming thanks to the pick-shaped stylus, the touch screen lacks the tactile "click" feel that comes from either flipping the strum bar on the console versions or actually picking a real string. It's easy to pick at the wrong area when you're not looking, causing alt-strummers to gape in disbelief as they mysteriously miss a series of eighth-notes because their first touch didn't take.
These are two large problems that are severe enough to hamper the fluidity of the gameplay. It is in this sense that the game doesn't always "work." Neither of these problems are necessarily anyone's "fault", instead being due to the nature of the hardware, but surely improvements can be made for the next go round. (How about an anchoring mechanism to keep the grip in place, and less finnicky strumming code?)
The other gripe you might have is hand cramps. Holding your hand in this new awkward position will definitely introduce some pain, and while "omg hand cramp" is a flippant complaint often used by Nintendo DS detractors, it actually does hold true here.
If you can tolerate these issues, then Guitar Hero: On Tour can be just as fun as the console versions if you come in expecting lower-quality sound files and a reduced tracklist. Hammering a tricky solo flat-out works here, and is just as satisfying to your fingers as it is on the console guitars. Shouting at the mic (I prefer clearing my throat) is a serviceable way of activating star power for the score junkie in you, and even though you don't quite feel like you're playing a fake guitar, you still feel like you're pulling off some mean feats when you play on Expert.
All told, Guitar Hero: On Tour is a viable option if you really want Guitar Hero in the car. It plays and feels enough like its console cousin, and is a commendable effort by the developer. Its mechanical issues simply cannot be ignored, however, and you need to be ready to handle them if you're going to plug in.
