Most of the games aren't too great, but Tanks is reason alone to rent it.
So, I rented it, and popped it into my Wii. First off, I saw that your Mii selection is much like Wii Sports. I picked my Mii, then started playing it. The first game was much like Duck Hunt for the NES, only with better graphics and no annoying dog. I played it a few times, it was okay. After playing through numerous other games, like table tennis (bad) to pool (quite fun once you figure it out.) The final game was Tanks. I have to admit, going into it I was not expecting much, but a few levels in, it got hard! Even though it got hard, it was very addicting! I called a friend over, and we played the crap out of it.
So, my final thoughts are...
Since if you buy it for fifty dollars, and it comes with a Wii Remote, if you have money to burn, then by all means buy it. All others, rent it if you have a friend stopping over. It is worth renting.