I'm quite fond of my FCXUno, but I did change a few things: front cantilevers, tires, bars, stem, brake levers, seatpost, seat, chainring, freewheel, and pedals

Some folks hate the wheelset, but I found the Jalco rims and unbranded hubs really aren't that bad (once properly trued). The wheelset is under 2 kg with freewheel, fixed cog, and track nuts.
The geometry is a little odd for a CX bike ... it's actually more track-like with short (405mm) chainstays and low trail. It makes the bike feel really nimble, but it can be a handful in sand/mud or on a fast descent. The frame has all the expected qualities of a 4130 steel frame - smooth and lively. I don't notice much flex, but I'm not a heavy or particularly powerful rider. The bike is a bit heavy - 23 lbs out of the box for a 54 cm. Shaving a pound off is pretty easy, more than that will take more substantial changes.
Quality is what you'd expect from BD. It's not a piece of garage art, but it's good enough to rack up plenty of miles without major problems. The brake levers are the only completely intolerable component. Other stuff is ok, but not so nice that you'll feel guilty about upgrading it
I use the bike geared 44:22 or 44:20 (depending on the course) with CX tires for Cyclocross racing in the fall, and geared 44:17 with commuter tires as a recreational SS bike the rest of the year. Overall, it's a fun bike to ride and is a great all-purpose FG/SS for the price. And if you enjoy pain, you can take it to the nearest CX race and have some real fun.