Overall Feeling:
Resident Evil: The Mercenaries 3D is kind of the definition of "short and sweet." While there isn't much in terms of gameplay or story, there's enough to keep you entertained for short-term gaming sessions of a few minutes or an hour. Improving on your score, trying new characters and buffs will give you the option of replay... but if you're someone that doesn't dig on beating their own scores over and over, you'll lose interest rather quick.
The Pros:
+Quick challenges for fun short-term gaming.
+Controls translate well to the 3DS new button/stick layout.
+Plenty of unlocks to bring interest into replay
+Addictive short-form gaming that leads to self-competion in the long-run.
The Cons:
-3D is easily lost (more so than other titles on the 3DS).
-The game is SUPER short.
-No option to delete save file so sharing/reselling the game isn't likely.
Whenever a new platform is released, from Nintendo in particular, the first response from the majority of publishers is always to post out smaller, bite-sized, mini-game-esque test games to get an idea of how their tech can integrate with the new platform. Most ‘hard-core’ gamers will immediately dismiss these titles, and wait on something for a little more substance.