I've had nothing but good experiences with WP7.5 software, which leads me to believe that WP8 could be worth considering. That said, I'm waiting until/if RIM manages to get their BBX hardware out before using my next contract upgrade, as I'd strongly prefer a phone with a hardware QWERTY board. On two different WP devices (HTC Surround and Samsung Focus), the software performed faultlessly. That said, one of the primary concerns for many users (apps) is a non-starter for me, since the only apps I require are an RPN calculator and Facebook (a necessary evil). [All I really want is good call quality, decent battery life, email, calendaring, and a bit of light web browsing/photography). Frankly, WP7.5 was near, if not at the top of, my mobile OS experiences, which include: WebOS (Palm Pixi Plus, HP Veer), iOS (iPhone 4 and original), Android (1.x and 2.x on HTC Hero, Motorola i1, Samsung Captivate), Symbian S60 (Nokia E66, E90, 6650), Symbian UIQ (SE P800, M600i), Blackberry OS 6 (9800), WM 6.0 (iMate Ultimate 8150, Toshiba G910), etc., along with the WP7.5 devices. My other favorite was WebOS, but it was really too buggy.
So...erm...I spend far too much time on phones. And Windows Phone is really pretty good (this coming from a former Apple evangelist (they lost me after Snow Leopard)/Linux user who tolerates, rather than enjoys Windows.