Great for the cost.
-.5 for simplicity, although this is also part of its charm.
-1 For a lack of features and that "something-is-missing-here" feeling.
Difficulty and time spent:
Extremely easy, unless you are going for a high score in which case it is rather challenging. The difficulty really rises when you hit over 20000 points.
Gameplay:
You are a bird. Your name is Pyoro. You want to eat beans. You stick your tongue out and get the beans. Simple, yet great for that long car ride or when you just don't feel like doing your homework, a great time consumer. You sure get a bang for your buck though, $2 for an addicting little game that you'll end up spending anywhere from 1-15 hours on.
Summary:
Not a GREAT game, if it was say, even $20 I'd pass it up, regardless of the extra gameplay mode. However, for only $2 this game is amazing, I've bought $30 games that took me a day to beat, but this $2 game has kept me entertained for many a 5-15 minute spurt. I recommend this game the second you enter the DSi shop.