Gunman Clive is one of the best games on the 3DS eShop. I really enjoyed my time with it (especially with the secret character), and for just a few bucks, it's a complete steal.
At the same time, it did have a few major glitches that detracted from the experience on the 3DS. Namely, the dreaded "second boss crash."
Upon reaching the second boss fight on level 10, the entire game would crash, and force a full 3DS restart. This happened to me a number of times, only to find out days later that turning off your 3DS' 3D slider would help solve the issue.