I first owned an HTC Trophy with Mango with Verizon, but returned it after a week and got an HTC 7 Pro through US Cellular because they have better family plans and, at least in my town, better customer service. So I can compare the two.
I'll start with the bad, and then get to the good.
THE BAD:
The first thing to realize about the 7 Pro/Arrive is that it really does have a small screen. 3.6" doesn't sound much smaller than 3.8," but you can see the difference. In fact, while playing Bejeweled, I sometimes touch the jewel next to the one I wanted, not a problem I remember with the 3.8" Trophy.
Also, it's a somewhat heavy and thick device. This is an inevitable result of the sliding keyboard.
Third, viewing angles aren't good. Colors are vibrant when viewed head-on, but wash out quickly when viewed from an angle.
Fourth, the volume, power, and camera buttons all feel less substantial and precise than the buttons on the HTC Trophy.
Fifth, app selection sucks compared to iOS. There are some great Microsoft apps (XBox Live games, Microsoft Office mobile apps, plus the built-in mail and calendar apps are fantastic), but third-party app selection just can't compete with iOS or Android right now.
THE GOOD (because, despite those five things, I looooooove this phone):
The operating system is nothing short of fantastic. It's intuitive, simple, and attractive. It's versatile, too: my tech-illiterate wife can use the phone just fine for social media (we actually have matching his-and-hers 7 Pros), but I can also use it effectively for work (emailing, Microsoft Office, mobile version of Westlaw Next), as well as gaming.
The slide-out keyboard is a dream. Key actions are crisp and precise. I can hammer out emails like nobody's business. This is a really, really good keyboard. Touchscreen-only keyboards like those on the HTC Trophy and similar devices are fine for status updates and tweets, but just can't compare for five-paragraph emails.
The angled screen when the keyboard is slid out is great--makes it far easier to read the screen. The hinge feels durable too. Nice touch.
If you have a $10/month Zune subscription, you can pack it full of music you've never purchased, including new hot releases, and continue listening to as many albums as you want without buying any of them so long as you pay your monthly Zune subscription. After the demise of Zune hardware, Windows phones are the only portable devices where you can play Zune downloads. I've got dozens of albums downloaded for free from Zune, and I download more everyday (sometimes just to see if I like the album), and I'm not paying a penny beyond my $10/month subscription. Fantastic.
Call quality is very good. Clear with no feedback.
The camera, while not "great," is definitely "good." The one trick is that you need to hold the button-down halfway until you see the autofocus snap into place; otherwise the image won't be focused. But once you learn to do that, you can get some pretty decent pictures. Facebook integration for posting the images and videos works beautifully, by the way.
CONCLUSION:
The 7 Pro/Arrive is not as stylish as some other smartphones on the market, but it works well, it's versatile, it's practical, it's well made, and it's inexpensive. Plus, you can use US Cellular with it, lesser-known than Sprint/AT&T/Verizon/etc, but fantastic with coverage in the rural US, and generally well-liked by people who have it, in my experience.