This is certainly right up there as one of the best FPS games on the Wii, although the competition is not exceptionally strong on this platform given that most of those titles are ports of popular franchises with wii controls tacked on and networking features greatly removed.
Without getting into the storyline (this can be read elsewhere) this is a fairly standard shooter with no real surprises but it may help to fill a void felt by more hardcore gamers who own a Wii. I found myself constantly shifting between motion + and classic controller control methods before finally settling on using motion + controls, although the benefits for this I found to be fairly minimal, it does offer a slightly better experience overall once you have got used to it.
The environments look a bit more interesting than in previous versions and it is usually pretty clear where you need to get to next. The boss battles were a little long for my liking but reasonably interesting. Overall the single player experience is a little short but is a bit better than the previous game.
The multiplayer has all of the usual game modes one would expect and allows up to four players to play locally too. There is a great deal of customisation available and overall the experience is good. There is also an on-rails shooter section to add some more variety and this is a welcome addition.
Overall, I would say that this is a game that you would be better off renting unless you are really keen to try and get your FPS fix on Wii.