Lacking fun and substance, it seems that the cheapest 3D eShop game may also be the worst.
Originally priced well below any other 3D eShop game, Bird Mania 3D brings back memories of the cliche phrase "you get what you pay for."
A constantly moving side-scroller, Bird Mania pushes players forward as they avoid trees, dash through enemies, and build points by collecting stars and popping balloons. As the player gains more distance, the game speeds up, making collecting and avoiding much more difficult. It's a high-score-building arcade-style game; so basically, you keep playing until you get hit by an enemy or a tree and subsequently die.
Unfortunately, beyond that, there isn't much to it. This might be unfair to say about such a cheap game, but the artificial difficulty only comes in the game speeding up and provoking a loss of focus, no doubt furthered by the unimpressive-yet-distracting 3D. Bird Mania simply does not give a feeling of accomplishment, or even fun, for doing well.

I was originally impressed when I saw that this game had a story mode. However, it's not a "story mode" per say, but rather a mode that coincidentally has story in the title. The difference is that in the latter, it’s acceptable to include no gameplay in the mode, and to instead include game credits and a disconnected slideshow explaining the plot in a few sentences before kicking the player out into the main menu. If that wasn't bad enough, the actual text likely wasn't even edited before publishing, containing strange uses of grammar and unnecessary capitalization. Here's one example: "Mojo overslept and has to Begin a crazy chase over fellow Birds". Don't worry; you have about as much context as I do. If anything, the plot, involving Mojo oversleeping and having to find his friends in Africa, actually worsens the experience of the game once you realize the horribly depressing truth that the game itself only ends when Mojo falls to his death (confirmed with an unmarked "R.I.P." tombstone after each finished round).
Outside of the "story" and the main mode, there are achievements, tasking the player with killing a certain number of enemies in a round or getting a specific amount of stars during the day. The shame with these achievements is that they simply exist, and actually obtaining them doesn't seem to do much for the actual gameplay outside of a check mark next to the achievement. Without incorporating the social aspects of Xbox Live or the ability to unlock content, such a mode feels silly, useless, and out of place. The achievements in Bird Mania are more difficult than the game is enjoyable. I spent 30 minutes trying to get one achievement, done so not out of addictiveness, but rather feeling the need to discover whether the fun of this game was somehow hidden underneath the tasks. They aren't. There's also a high-score board, but it's not an online one, so it’s not terribly interesting.
Bird Mania 3D is not a fun game. It is repetitive, lacks the addictiveness of other high-score-focused affairs, has an insult of a story-focused mode, contains no substance outside of a basic mode, and does nothing to convince the player that a good purchase was made. That's all there is to it.