Having both models, it is kind of surprising how different they are. Depending how you felt about the first model, I could see how you could be disappointed in the second one.
For me, being able to use the ATV1 without using my computer was a big deal. I used it for watching Video Podcasts (synced from my computer), Renting movies, and listening to music - always without having my computer turned on.
This is one of the biggest benefits of the ATV1 for me. It makes it feel like an part of my A/V system not a computer.
I know some people hate the syncing, but that just wasn't an issue for me. I sync my iPhone daily, and download podcasts daily, so the syncing of the ATV1 was pretty much transparent.
The benefit of the ATV2 is all about streaming, and Netflix. Streaming over the net, or streaming from your iPhone or iPad. For listening to music, or watching Video podcasts, I find that I can simulate the ATV1 experience by syncing the media to my iPhone/iPad and then playing from there - again keeping my computer out of the playback process.
One drawback is that now I need to have room on my iPhone/iPad for the video podcasts. I know I could stream them from the net, but I like iTunes managing my subscriptions, and keeping track of which episodes I have watched.
Since I purchased my ATV2, I hardly used it except to try out Airplay, and to do some $0.99 TV rentals. For me, I purchased the ATV2 for its POTENTIAL - hoping that we might have downloadable apps some day.
Unfortunately, my ATV1 died last week so now I have started to use the ATV2 a bit more. It works well, but for me, not as well as the ATV1. My ultimate solution would be an ATV2 with 32GB of flash and the option to sync media to the device or stream. Make it $199 and it would be a slam dunk.
As it stands now, my suggestion would be to look at how you use your ATV1 and how happy you are with it. If it works for you, then I would suggest you stick with it, and look at the ATV2 when you find something the ATV1 doesn't do for you.
If you have issues with the ATV1 (i.e. can't stand the syncing, etc), or want Netflix, etc, then by all means go for it and get an ATV2.
For me, the ATV1 was a better device for what I used it for and the way I want to use it.