Shortage of apps? well there are well over 13k and growing, growing at a faster rate than any other platform as well.
If you like a large screen then the HD7 is one of the best WP7 devices plus they have just released the HD7S but I do not know the availability of it but it has a better screen. Saying that though I've never had any real problems with my HD7 and I can say it's the best device I've ever owned.
The OS is smooth, reliable and while first impressins you may think it looks basic, it's not, it's more to the fact that it works in such an easy way you find the "trying to be pretty" eye candy was just a waste of time and slows the system down.
With the recent update as well the phone if faster at loading than before and I'm looking forward to the next update later in the year.
The best bit about the update is the backup and restore, one the update has finished the phone is back exactly as you left it with all your apps, games and messages etc all where they should be, no more having to reinstall this or that it does it all for you.
Back to devices if you liked the Dell there is the Dell Venue Pro with it's Gorilla Glass (one thing the HD7 does not have but other devices do)
As far as I'm concerned WP7 is a pleasure to use.