I won't bother you with what Guitar Hero is, nor will I bore you with details about how the game is played, or whether it plays well. Yes, it plays well, and yes, it is same as it always has been, press the note on the bars then strum when the according color passes the bar. However, there are some new additions that make Guitar Hero 5 the best Guitar Hero yet.
Party play is long overdue, and something that was almost added into Rock Band 1. Party play is just that, a mode for a party. Now, in between keg stands and beer pong, you can pick up and play a song. Drop in and drop out support works really well and you won't fail out of songs if you decide you don't really want to play. You can even choose your own play list and select your own tracks. The tracks play random by default, and any instrument can drop in and drop out at anytime, including vocals.
Another new feature is the ability to play any mix of instruments that you want. 4 guitars, 4 mics, 4 drums, 2 guitars and 2 drums, anything you want you can do. I find that the screen gets a little cramped if you decide to do 4 instruments, especially on an SDTV, however it's finally fun to be able to play against each other without having to do competition mode.
Another great new multiplayer feature is the Rockfest mode. The Rockfest mode includes different modes of play that spice up the play. Momentum, which was one of my favorite modes, starts everybody off at medium difficulty, playing well increases the difficulty (and the score) and playing poorly decreases the difficulty (and the score). It's also a great mode to start off with newbies, as they can find and play the difficulty best suited for them for any given song. Elimination is another fun mode. It's a knockout style mode with the lowest scoring player getting eliminated at marked points in a song. Rockfest can be played online or locally, and is a really nice addition to GH.
Song specific challenges exist as well, adding bonus points for doing certain things during certain songs. These can range from streaking (perfectly playing) a certain amount of notes by strumming up, or using a whammy bar for a specific amount of time. These can add stars to your score (usually 5 stars is the max, however you can get a total of 9 depending on how you play) which net achievements/trophies on the 360 and PS3 respectively.
Don't worry if you've downloaded tons of GHWT DLC, most of the music (the only music they couldn't put in was because of licensing issues) downloaded for WT will be fully compatible with GH5, you just need to download a free patch before you use it.
Much of whether you will buy GH5 is determined by whether or not you like the music in it, however GH5 is by far the best iteration of the Guitar Hero series yet.
Guitar Hero 5 releases today, September 1, 2009 for the PS3, 360, Wii, and PS2.