Here's some of the apps I have and like:
Pac-Man - It feels like the real thing!
Last.fm - Pretty sweet interface
Shazam - Works well at finding songs
Ringdroid - Maybe the best made app of all, turns any audio (music, voice recording, etc) into a ringtone
Skymap - Uses the compass/mangtometer to tell you what constellations you should be able to see. Pretty neat.
Compass - Just a visual compass. I like it
Stopwatch - Comes in handy
Bubble - It's a level, on your phone. Already used it to straighten out a crooked painting in my living room.
Power Manager - Has differnent power profiles that get applied situationally, helps with battery life tremendously.
Toggle Wifi - For turning wifi on and off with one click. Very useful.
Flashlight - makes your screen 100% white and 100% brightness, it is really ridiculously bright.
That's just a few that I liked.
The things I really like are the widgets. I have a couple of picture frames on my left and right home screens to give them some character. And I like the flexibility to put a shortcut to just about anything on your home screens. It's infinitely customizable.
The GPS works great, although I only turn it on once in a while. Using it all the time will KILL batteries. And I find that I'm turning 3G off most of the time. If I'm somewhere that I want to browse the web, I'm usually around a wifi network I can use, which is faster than 3G anyway.
And I really like the call quality. No dropped calls, and the speaker/mic seems to be very good. Much better than my blackberry on both ends.
There are some gripes the - the cut and paste function currently only works in text entry situations, so no more looking up quotes on IMDB to text friends like on my blackberry. I had a bit of trouble synching my contacts with gmail - but that might be because I had about 500 useless contacts in my gmail I should have gotten rid of. And a visual keyboard would be nice. I hear the rumored "cupcake" update should fix some of those issues, but there's no real concrete date that update will go live.
Anyway, about 4 days in and I like it a lot, although I still kind of miss my blackberry.