Is this for a "see, WP7 users feel they are using an OS that lacking what iOS and Android have," or is it for "WP7 users really like their phones, and here are some apps they'd like to see added in the future" kind of thing?
Does it matter? Either way, the answers should be the same. Let's not spin this here. Windows Phone 7 is an awesome OS objectively, subjectively it is my favorite of the bunch, but the one aspect it really still needs to catch up on is app support. Microsoft has been doing well in this regard, pushing development forward and getting good apps on board, but there is so much intertia for the iPhone and Android in this department that there's still plenty of work left to be done.
I'm not coming from an iPhone or Android but rather WM6.5. As such, I have a slightly different perspective than most. I don't "miss" apps I had on previous platforms. Instead, I find myself disappointed at times that apps I hear about and want do not exist for WP7. Here's my short list of apps that I've found myself wishing had been released for WP7 as well as iPhone and Android:
1) HBO Go
2) Optimum App (only useful for Optimum cable subscribers)
3) ESPN Fantasy Football
4) NY Giants (which even released for Blackberry but not WP7, and it JUST came out!)
Hm, that's all I can come up with now. I know there have been others but I can't come up them at the moment. I guess that means they weren't
that important to me to begin with.
EDIT: That nagging feeling I had that I was missing apps wasn't actually about missing apps but missing functionality in apps. This should improve with Mango APIs, but nonetheless is currently lacking. Biggest example here is access to native hardware. For instance, no SkyView-style app like the iPhone has is currently possible without Compass and Camera API access. Also, deposit by picture in my BoA app is missing, again likely due to lack of a Camera API (though I wonder about this, as the Walgreens app allows refill by scan pre-Mango).