Just prepare yourself for the loss of functionality. Windows Mobile was a very mature, and very optimizable, feature rich platform. Windows Phone is very streamlined, beautifully designed and intuitive to use. However, its a newer OS so certain things are inevitably missing as of now.
The Mango update is bringing quite a few things I was hoping for in Autumn (sockets support for things like Instant Messengers ect, multitasking, quick resuming of apps....they will announce more of the consumer end of things at a conference in Fall), but you will probably never see as much functionality as you have been accustomed.
That being said, is it worth it? Yes. Unless you absolutely need certain things (like real tethering......the focus can usb tether through a dial up, but its through an AT&T connection and will be easily charged to your account if they catch you). I came from Android which, is actually a lot like WinMobile. I miss things, but I wouldn't go back for anything.
The app situation is great. Most everything you need is there, with some more 'official' apps (like New York Times) coming soon. Developers and companies alike have realized windows phone is here to stay, and is a surprisingly nice platform to develop for, and the marketplace is growing pretty rapidly.