I honestly don't get the attraction either. It was cute for 5 - 10 minutes then the fun fades and I haven't picked it up since. (I'm more of a Plants vs Zombies person myself).
Don't get me wrong, I'm glad for Rovio's success and its nice to see people enjoying the game but for me it wasn't that big of a deal.
I am actually one of those who likes both games. Sometimes I lean toward tower defense games and PvZ scratches that itch, whereas AB does the same for physics gaming (that and Osmos - GREAT ambient sound effects and music there).
Games I revisit are the ones where the controls feel right, or the gameplay is intuitive to pick up, or the graphics are compelling.
I went through most of the Cut the Rope levels and got bored fast. Same with Fruit Ninja. Spider was beautiful, and more great music, but got repetitive. Nanosaur was a game I loved on the Mac, so I thought Nanosaur 2 would be awesome, but it suffers from poor map layout (over a year and still haven't gotten past the first level!). A-Breaker is new to me, and a good physics game. CroMag Rally, another game from the Mac, the physics of handling the cars doesn't translated over well to the iPod.
I picked up Rage HD and of course it's gorgeous, but I don't like rail shooters, so I bored of it. Zombie the Apocalypse is kinda cool, but has some frustrating navigation moments. Dead Space was awesome, until I got lost. iBomber Defense is cool! One of my favorite tower defense games. Battleheart, great light version of an RPG with some stats management, Duke Nukem 3D - are you kidding me? Had it on the Mac, had to have it here! Great retro feel to it. Dark Meadow is kind of fun, but half the time I wonder if it's designed to take me back downstairs once I've made it upstairs but meet my maker.
I'll probably pick up Marathon and Baldur's Gate too. I'm a sucker.