Alright, so the people have spoken!
Global High Scores:
I've started considering using Scoreloop (www.scoreloop.com) as an online high scores provider. This would come with the sacrifice of some user privacy. Permissions would also have to be added to the game (Internet, read contacts, and read phone state and identity). I've asked the folks at Scoreloop if I would be able to include a preference to disable the integration of these features for the people that don't want them. I hope to hear back from them soon.
Privacy aside, integrating with Scoreloop presents a good opportunity to add not only high scores, but achievements, challenges, and other social interactions. Doing this all myself would take much more time.
Feel free to comment on any thoughts you have on this!
1. More maps are on the way for the full version.
2. More information will be provided on the map choosing screen. Indicators for having completed the level on easy, normal, or hard, as well as your current high score for that level.
Down the road:
1. I'd like to add a feature to fast foward the game.
2. Rather than more tower types, I'm toying with the idea of adding bonuses at certain score values. The bonuses would be enhancements you could place on top of towers to increase range, damage, or speed. Or one could simply trade the bonus for more energy. Another possibility is having the bonuses be towers themselves that add those increases to the towers around them. Something similar to this is very common in other tower defense games.