The Samsung Focus S has a tough time competing against smartphones that aren't running WP7. The iPhone 4S is available at the same price with a dual-core processor and 10-times more apps.
Up against other WP7 phones, it's easily among the best choices in its price range. Its only real competitor here would be the HTC Titan, though the Nokia Lumia 900 may be worth consideration.
It really comes down to your feelings towards WP7. It's very easy to hate if you don't give it a fair chance, but after a week or two with it, you might find it hard to go back to Android or iOS.
WP7 is something unique with all sorts of clever features and amazing integration that you don't realize you've been missing until you give it a try.
The Super AMOLED Plus display really does stand out against other WP7 devices.
Even with a large, 4.3-inch display, the Focus S is very thin and extremely light.
The unique experience carries a hefty learning curve, and focusing on all of those clever features and integration seems to have resulted in overlooking some of the fundamentals.
Zune software is required to transfer anything to or from the phone, and even with it, most file types are simply off limits.
The app market still has long way to mature.
AT&T's "4G" network is a complete let down.
If you want to give WP7 a shot, the Focus S should be one of your top considerations. It'll go head to head with any other WP7 phone on the market, and it does it in a thin, light, and sleek package.
It also makes a great choice for anyone looking to upgrade from a Blackberry, Windows Mobile, or WebOS device; however, that's not to say an iPhone 4S or Samsung Galaxy Nexus wouldn't be an equally valid upgrade.
Anyone coming from iOS or Android will really need an open mind if they don't want to wind up smashing the Focus S out of frustration.
Just make sure AT&T's network is solid wherever you'll be using it most.